The authors studied multiple parenting cognitions and practices in European American mothers (N=262) who ranged from 15 to 47 years of age. All were 1st-time parents of 20-month-old children. Some age effects were 0; others were linear or nonlinear. Nonlinear age effects determined by spline regression showed significant associations to a "knot" age ([around]~30 years), with little or no association afterward. For parenting cognitions and practices that are age-sensitive, a 2-phase model of parental development is proposed. The findings stress the importance of considering maternal chronological age as a factor in developmental study.