It has previously been shown that having an older sibling may influence language skills, with children who do not have an older sibling showing greater language scores compared to children with one older sibling (Havron et al., 2019). Closer looks at the characteristics of older siblings such as age gap and sex demonstrated an effect of older sibling’s sex. Specifically, children who had an older sister had better language scores than children who had an older brother with their language score not differing from language scores of children with no older sibling (Havron et al., 2019). In our replication study (Study 1, https://osf.io/d73yv/?view_only=a4c8f42625a84d38a23664bb8cb9e0c1) with the GUSTO cohort of children from Singapore, we replicated the finding from the EDEN cohort study (Havron et al., 2019), thus demonstrating better language skills in children with no older sibling compared to children with one older sibling. Unlike in the EDEN study, we have not replicated the effect of older sibling’s sex on children language skills. In this study, we are conducting a follow-up of our replication study by assessing the effects of other factors that may influence the language skills in our GUSTO cohort. One of the reasons proposed by Havron et al (2019) for the effect of sibling sex is maternal stress. The logic behind this claim is that maternal stress is related to poorer language scores (King & Laplante, 2005; Laplante, Brunet, Schmitz, Ciampi, & King, 2008; Laplante et al., 2004) and it has been found that raising a female baby is related to less maternal stress in comparison to raising a male baby (e.g., Scher & Sharabany, 2010). In order to investigate this possibility, as a first step in our follow-up study, we will assess the effect of maternal stress and the presence of an older sibling on language skills. Next, we will examine the effect of maternal stress and the older sibling’s sex on language skills. We explore the effects of maternal stress and older siblings on language skills in the above-mentioned GUSTO cohort. In this cohort, language measures were administered in four different languages (English, Mandarin Chinese, Malay, and Tamil) depending on the participants’ native language.