This study evaluates sources of individual variation in child pretense play as an expression of emerging mental representation. Family sociodemographic characteristics, maternal personological characteristics, and maternal affective and cognitive play behaviors, as well as children's gender, language competence, and play, were examined simultaneously. Naturalistic child solitary play and child collaborative play with mother were videorecorded in 141 20-month-olds. Child solitary play, child-initiated and mother-initiated collaborative play with mother, and maternal demonstrations and solicitations of play were then coded into nonsymbolic and symbolic acts. Zero-order relations obtained between child play and, respectively, child gender and language, family SES, and maternal verbal intelligence, personality, physical affection, and play demonstrations and solicitations. Structural equation modeling supported the following unique predictive relations: Child language and mothers' symbolic play positively influenced child collaborative play, and child gender and mothers' verbal intelligence predicted child solitary play. Child gender and mothers' verbal intelligence and physical affection influenced mothers' play and so influenced child collaborative play indirectly. The cognitive advantages of child play and maternal influences on child play are placed in an adaptive parenting framework.