Childrearing behaviors are often shaped by familial and cultural principles that function as guides for socialization goals and effective childrearing practices. For an increasing number of Latino families, the extended kin often acts as a source of childcare support. Due to a scarcity of research on the familial support configurations of Latin American families, the current study utilizes a cross-cultural retrospective approach to explore the associations between matrilineal/patrilineal kin and life history strategies in relation to childrearing. Applying a family system and life history framework, the present model tested 200 university students from Mexico and Costa Rica on measures of family emotional environment and traditional social values (e.g., familismo/simpatía and patriarchal values). Results found that childcare assistance from patrilineal and matrilineal kin was associated with positive family emotional environment, which weakly mediated the association between kin care and slow life history. Positive associations were also found between matrilineal kin childcare and traditional Latin social values. However, patriarchal values were only predicted by higher levels of patrilineal kin aid. The results are consistent with the general theoretical literature of life history theory and family systems theory, suggesting that high levels of childcare produce positively emotional family climates, which in turn perpetuate the development of prosocial individuals with slow life history strategies. Implications for further research are discussed.