Family and its language are one of the most important domains when it comes to acquiring a language as a mother tongue. Fishman argues that the family acts as a united front against external pressures, and the language of the family is the inevitable ground for this ^[1][14] (p. 94).

Acquiring a language in early childhood is already a complex process itself; it becomes even more multiplex when there is more than one language to acquire, for example, when parents speak different mother tongues or when it is typical for a multilingual region such as Belgium, Switzerland, or India. Here rises the importance of FLP, which, as the name suggests, is the established language policy used within family. In earlier years of researching FLP, it was defined as “explicit and overt planning use of languages in relation to language use within the home and among family members” ^[2][6] (p. 907). In 2017, the definition was revised, and the two most important adjectives acquired the opposite meaning by defining FLP as “in fact implicit, covert, unarticulated, fluid, and negotiated moment by moment” ^[3][15] (p. 322). This shows that if one plans the usage of languages at ideological level, then management and practice might differ. This shows how complex FLP is and why any research conducted in this area is and will be a tremendous help to further research.

FLP becomes more and more important and distinct when discussing it at different levels; first is the macro level (LP level), then there is the meso level (includes groups, organisations, communities, political parties), and the micro level, which is individual level and includes families and relationships ^[4][16] (pp. 52–53). The micro level is considered very important as it has a crucial role on children’s sociolinguistic environment ^[5][17] (p. 172). Yates and Terraschke claim that the meso level has a significant role for a minority language within society. Communities and their activity are important sources for multilingual families in cultural contexts and for preservation of their heritage languages ^[6][18] (p. 107). On the state level, LP level gains importance to the prestige of the minority language in the host country (for example, teaching it in school) and language prestige around the world ^[7][19] (p. 225).

Bernard Spolsky connects many aspects with FLP: political, social, demographical, religious, cultural, psychological, and bureaucratic, etc. He emphasises that FLP exists even when it has not been expressed clearly to the outside world ^[8][9] (p. 6) Spolsky also says that there are many factors which influence FLP. These include, for example, family structure, assimilation, parental education, language action, and cultural identity. Considering family structure, he means that in case there are older siblings in family, then they will most certainly have an effect on younger children’s languages ^[9][20] (p. 433). Zhu adds that when older siblings penetrate mainstream society, then, willingly or not, they affect younger children’s fluency and motivation with relation to their heritage language ^[10][21] (p. 175). There is research conducted on how older children in family contexts influence younger children’s language, and more and more evidence surfaced suggesting that older siblings influence younger siblings toward using the mainstream language (see ref. ^[11][22], and references therein). However, there have been opposite outcomes in the heritage and mainstream languages when parents insist that older siblings shall speak only in a heritage language with other family members ^[5][17] (pp. 173–174). In case there are grandparents who insist to speak in their heritage language in the family structure, then the possibility to preserve heritage language is more likely as well ^[12][13][23,24].

Assimilation and cultural identity are closely linked. Regarding assimilation, it shows that when parents introduce children earlier to the mainstream language and culture in their sociolinguistic environment, the more prone they are to assimilate. Then, the culture starts to play a role—parents who have a strong connection to, awareness of, and pride for their heritage language could even slow down children’s assimilation to mainstream language ^[14][25].

Parental education also plays a role in FLP. Although there are controversial studies in some means, for example, one study indicated that parents that are more educated are more likely to preserve their heritage language while another study suggested that parents with lower education find it harder to assimilate to a mainstream language, which means that their heritage language is better preserved for their children ^[15][26] (pp. 407–408). These two studies seem to have come to similar results, despite the different socioeconomic or educational status of the parents; this suggests different motives for preserving the heritage language. Spolsky adds that the success of FLP, i.e., the parents being able to effectively transmit the heritage language, is influenced by parents’ language awareness ^[16][4]. Parental language awareness is an important part of language policy that practically influences children’s language acquisition ^[17][27].

Under the language action, it is meant that parents literally need to take action to transmit a language, especially when children hit their teens, as they are becoming more independent, including their language choices ^[18][28] (p. 119). Intervening, such as enrolling children in heritage language classes, might be emotionally intensive and energy consuming but necessary if parents want to preserve their heritage languages as the minority languages ^[19][29]. This confirms the complex FLP model and illustrates how difficult it might be for parents to raise bi- or multilingual children.

Doyle states that all family members usually valorise bilingualism and family language. He also says that all family members are co-constructing the FLP. Doyle’s research shows that younger children sometimes showed resistance to communicate in a non-societal language. The latter happened more when one of the parents could not understand the non-societal language (refs. ^[20][21][30,31] had similar results). He also brings out the fact that Estonian is a rather small language on the global scale, meaning that it provides fertile ground for larger languages to penetrate the sociolinguistic landscape thereof ^[22][32] (p. 9).

Tannenbaum discusses that the reason why bilingual families have a FLP and follow one of the possible FLPs described, for example, in ref. ^[23][33], is that parents want to keep the contact between children and heritage and to protect the unity of the family ^[24][34]. Baker says that the attitudes of people using language have the greatest effect on its maintenance or language death in society ^[25][35] (p. 2), so the parents parenting in their mother tongue is vital for keeping their heritage alive inside the (extended) family. Not only the heritage on a macro level is at stake but also the micro level; in family relationships, a common language helps to create better bonds between family members and the absence of the heritage language in some of the family’s members could have a negative impact on the family wellbeing ^[26][36].

The most popular language approach in multilingual families—the one parent one language strategy (hereafter OPOL)—has been a widely researched approach in FLP. OPOL is a strategic decision that is made due to the birth of a child in bilingual family ^[27][37] (p. 696). As the name suggests, OPOL means that parents have different mother tongues but both parents have some sort of proficiency in each other’s languages. However, in refs. ^[23][28][33,38], the authors of which being the first linguists to use this terminology, no information concerning the competence of each parent in the language of the partner is presented. Döpke adds that one of the parent’s mother tongues in the OPOL approach is the dominant language in their sociolinguistic environment ^[29][39].

Unfortunately, there is no consistency in the OPOL approach regarding management, daily communication, and children’s language proficiency. Research shows that, for some children, OPOL has been very effective and they turn out to be balanced, bilingual individuals, while some children may show an unbalanced behaviour with respect to the mainstream language. They may further show signs of delay in some grammatical aspects with respect to monolingual children ^[2][6] (p. 913).

The attitude of parents towards the strategy influences greatly the success of OPOL. For example, Piller says that many parents believe that OPOL will surely lead their children to balanced bilingualism, while other parents believe that OPOL is an investment in their children’s future because it increases a child’s educational advantage by investing in desirable language skills. She adds that, even if considering those beliefs and attitudes, many families still fail to implement OPOL as parents rarely strictly adhere to the approach. Only a few families can stick to OPOL ^[30][40]. Lanza says that an OPOL approach is the most difficult to maintain, moreover when taking into consideration that the parents will speak with each other in one or two languages, presenting to the child that at least one of the parents has competencies in both languages ^[31][41]. Families might have difficulties implementing OPOL, as other (input) factors have to be taken into consideration when exposure to a heritage and a majority language is taking place ^[32][42].

More often, parents mix languages and bring in the expressions or/and terms from each other’s mother tongues ^[30][40] (pp. 67–70). This idea means, for children’s language acquisition, the emergence of translanguaging ^[33][43]. Studies have shown that the families that have the greatest success are those that strictly adhere to the OPOL, that is, where the OPOL is chosen, and where families do not share a common family language (ref. ^[34][44] and references therein).

For implementing the approach in best way possible, Lanza outlined six different parental discourse strategies and they are minimal grasp, expressed guess, adult repetition, move on, adult code-switch, and borrowing ^[31][41]. Lanza’s strategies are parental strategies that are used in order to “bring the child in a monolingual mode” when code-switching takes place. Döpke described translation and modelling strategies ^[29][39]. Those strategies help to carry out approach that parents have chosen, i.e., these discourse strategies help the parents to return to OPOL (one of several FLPs), in which they behave monolingually. The following is a brief overview of these strategies with constructed samples to better understand each strategy, which is helpful in better understanding the parent’s methods for implementing certain strategies in the current study.

Minimal grasp reflects the strategy where parents make believe that they did not understand what the child said, meaning that the child has used a language that is undesired by the parent ^[31][41] (p. 262). For example, if a child in an Estonian/Italian family speaks to an Italian parent and says (Estonian is in bold and Italian is in italics):

Expressed guess is a strategy where the parent “guesses” what the child has said in the undesired language, showing to some extent that the adult understood what the child said in the non-desired language ^[31][41] (p. 262). If to use a similar example as above, then the dialogue might look like this:

Repetition reflects the strategy where parent repeats the sentence in language the parent wants the child to speak. It shows either confirmation or translation about what the child has said ^[31][41] (p. 262):

Move-on strategy means that a parent ignores the child’s choice of language and responds in the parent’s preferable language. This results in bilingual conversation and shows that the parent agrees with the child’s chosen language ^[31][41] (p. 262):

Adult code-switch refers to a strategy where parent adapts to the child’s language. This shows that the parent is made to shift from their preferable language to the child’s preferable language ^[31][41] (p. 262):

Borrowing reflects to a strategy where the parent includes word(s) from the language that a child has used, showing that the parent understands and partially accepts the child’s chosen language ^[31][41] (p. 262):

Döpke proposed two more strategies, which were not listed by Lanza, but for this study are important to mention.

Translation request is when a parent requests the child to speak their preferred language, meaning that the parent does not accept other languages spoken to him/her by their child. This is more typical with children with greater language proficiency ^[29][39]. For example:

Modelling is a strategy where there are new words for the child and the child does not know how to express them or says them incorrectly ^[29][39].