Parent-reported developmental concerns can be a first step toward further screening and intervention for children at risk for ASD. However, little is known about the extent to which parental well-being and child behavior contribute to parental concerns, especially in families who already have one child with ASD. This study included 54 parents and their 18-month-old high-risk toddlers to examine the extent to which parents' well-being (i.e., parenting stress and self-efficacy), and children's behavior (i.e., expressive language and social communication) contribute to parents' concerns regarding their toddler's development. Results revealed that parental concerns were predicted by their own well-being as well as their toddler's expressive language, highlighting the importance of addressing the needs of both parent and child in intervention settings.