Nowadays, families migrate more frequently than ever before. Regardless of reasons for migration, it has a substantial impact on families in terms of their language, culture, and communication. The linguistic aspect is a key part of this issue, particularly in families with young children who enter school and have to develop a new language. There is a lot of research about the acquisition of a second language and the heritage language loss in an education context. This research focused on socio-emotional factors associated with first language (L1) maintenance and second language (L2) acquisition in a situation of migration in which both languages have implications for education. The relationship between second language acquisition and cognitive factors has been a focus of interest for many authors, but the influence of social and affective factors, such as parental attitude and cultural orientation on L1 and L2 acquisition has not been explored to such an extent. Moreover, Polish migrant families represent a non-traditional, more fluid type of migration, they often travel between their heritage and their host country, so patterns of language acquisition and influencing factors may also be different than those explored in previous studies. The purpose of the longitudinal study was to assess the direction and rate of development of L2 (English) and L1 (Polish) among the children of Polish migrants to Scotland who have just started primary school, and explore the social-emotional factors that might affect this. These consisted of the parents’ acculturation towards the mainstream (British) culture and language, enculturation towards their Polish heritage culture and language, selected family demographic features, and the children’s socio-emotional functioning as measured by the Strengths and Difficulties Questionnaire (SDQ) (Goodman 1997). Participants of the current study comprised 69 Polish children (37 girls and 32 boys) and the parents of 53 of the sample, resident in central Scotland recruited mainly through Scottish primary schools. There were three main research questions: (1) What is the rate and direction of development of L1 (Polish) and L2 (English) among the 4 to 6 year-old-children of Polish migrants to Scotland?; (2) In 4 to 6-year-old- children of Polish migrants to Scotland is acquisition of L2 and maintenance of L1 associated with parents’ cultural orientation towards Poland and Scotland, parental language attitudes to Polish and English, or socio-demographic factors?; (3) What is the link between L2/L1 acquisition/maintenance and the socio-emotional functioning of a child?; (4) What is the role of engagement with a language in the language acquisition of the 4 to 6 year-old-children of Polish migrants to the UK? The children’s L1 (Polish) and L2 (English) language skills were measured at the start of their first school year using two language proficiency measures (an English one and a Polish one). After 18 months the tests were repeated with the same cohort to give a measure of the change/progress in each language. Additionally, the parents of the assessed children completed the Acculturation Questionnaire, Strengths and Difficulties Questionnaire, and Family, Language and Attitudes Questionnaire created for the current study. In regard to Research Question 1, the scores at T2 for English were significantly higher than at T1. However, the overall group score for Polish was significantly lower at T2 than at T1. One key finding was that the Polish did not progress for all but 15 (around 21%) out of 69 children. By contrast, only five (around 7%) out of 69 children did not make any progress on English. For Research Question 2, there was no association between parental cultural orientation scores on either mainstream or heritage scale and the children’s total language scores. Similarly, there was no link between parents’ language attitude scores and their children’s total language scores. However, both cultural orientation and their language attitudes scores predicted the amount of the children’s engagement with a language. In addition, previous language exposure and current language use were in turn strong predictors of L2 language scores. In terms of L1, the amount of engagement with a language was affecting the language scores only in the form of one of its components: the current language use. For Research Question 2, three socio-demographic measures also played a role: children’s place of birth, their time in Scotland and parents’ education. The children’s country of birth (Poland or Scotland) had an effect on their L2 and the length of their stay in Scotland had an effect on both L1 and L2. The parents’ education level influenced their L1 performance in a positive way, but the link between this variable and the children’s L2 results was not straightforward as there was a difference between the effects of fathers’ and mothers’ education. Mothers’ education was strongly associated with the children’s L1 progress. For Research Question 3, the SDQ findings indicated that some, but not all of the SDQ sub-scales (Pro-social, Emotions and Behaviour) in different ways were associated with the children’s language scores. However, both heritage and maintenance cultural orientations of the parents were negatively correlated with psycho-social functioning problems of their children: higher scores on enculturation and higher scores on acculturation parental attitude scales were associated with fewer behavioural problems in their children. Additionally, the parental heritage orientation was associated with their prosocial behaviour. This suggests that parental attitudes do play an indirect role in children’s social adjustment. For Research Question 4, for both Polish and English, in line with current literature, the amount of engagement with a language contributed significantly to the children’s scores. The above findings indicate that although the link between socio-emotional factors and the children’s linguistic development in L1 and L2 is not direct, they do play a role in language acquisition. It helps build a more complete picture of a complex relationship between socio-emotional and cognitive aspects of bilingual child development, contributing to the knowledge of this issue in both research and practice.