We study the social integration of ethnic minority children in early childhood. We embed a randomized field experiment in a two-month Turkish preschool program for disadvantaged 5- year-old native Turkish and Syrian refugee children. Within each school, we randomly assigned children to classrooms with a low, medium, or high share of refugees, generating exogenous variation in interethnic exposure. We find that interethnic exposure fosters friendships and improves Syrian children’s Turkish language skills, with effects that persist into primary-school grades nine months later. We find no corresponding cost to the academic outcomes of native Turkish children. Our findings show that early-childhood classroom composition can shape integration in ethnically diverse early-education settings.