How children acquire their mother tongue has always fascinated scholars. However, for the most part, these studies have focused on children growing up with only one mother tongue, and mostly, in the United States learning English. Researchers of the Language Acquisition across Cultures Research Group at the Laboratory of Cognitive Sciences and Psycholinguistics of the Ecole Normale Supérieure and Heidi Colleran, leader of the BirthRites Research Group at the Max Planck Institute for Evolutionary Anthropology (MPI-EVA), collaborated to study how children growing up in a multilingual society acquire language.