Research into family context as a socializing agent points to the need to take parental beliefs into account due to the role they play in both parenting strategies and, ultimately, in the psychosocial adjustment of children and adolescents. The present study aims to explore possible relationships between parental beliefs about childhood and adolescence from a longitudinal and qualitative perspective. The beliefs held by parents of teenagers about adolescence are compared with those they hold about childhood at that same moment, and the evolution of these ideas is charted over the course of 16 years as their children grow. A total of 102 parents participated in the longitudinal study. They completed two types of semi-structured interviews: one of them throughout the entire study period and the other once their children became teenagers. The results reveal an association between the type of beliefs parents hold about childhood and their perception of adolescence, and they indicate that these ideas change over time as more adjusted and modern beliefs about child development correlate with a more positive perception of adolescence. These results are interpreted from the perspective of their influence on beliefs about parenting styles, reflecting what is reported in the recent literature regarding the most successful styles for fostering children’s and adolescents’ psychosocial adjustment.