Little is known about the development of self-regulation processes during the preschool period in autism spectrum disorder (ASD). How parental characteristics such as the broader autism phenotype (BAP) relate to children's self-regulation is not well understood. Preschool-aged children with (n = 24) and without ASD (n = 21) completed an inhibitory control task and mothers reported on child emotion regulation and their own BAP traits. Children with ASD had lower emotion regulation, and emotion regulation was a protective factor in the association between ASD and internalizing behavioral concerns. Lability/negativity was highly overlapping with externalizing. Maternal BAP characteristics were differentially associated with all self-regulation outcomes across groups. Parental factors should be considered in emotion regulation interventions for young children with ASD.