Many parents express concerns for their children's multilingual development, yet little is known about the nature and strength of these concerns - especially among parents in multilingual societies. This pre-registered, questionnaire-based study addresses this gap by examining the concerns of 821 Quebec-based parents raising infants and toddlers aged 0-4 years with multiple languages in the home. Factor analysis of parents' Likert-scale responses revealed that parents had (1) concerns regarding the effect of children's multilingualism on their cognition, and (2) concerns regarding children's exposure to and attainment of fluency in their languages. Concern strength was moderate to weak, and cognition concerns were weaker than exposure-fluency concerns. Transmission of a heritage language, transmission of three or more languages, presence of developmental issues, and less positive parental attitudes towards childhood multilingualism were associated with stronger concerns. These findings have both theoretical and practical implications: they advance our understanding of parental concerns and facilitate the development of support for multilingual families.