Childbearing has been increasingly delayed in Western countries. As older mothers are likely to be advantaged over their younger counterparts, the demographic literature has tended to view this demographic trend as potentially beneficial for child well-being. Conversely, less attention has been given to medical studies showing that giving birth at advanced ages is associated with health risks for children. This article uses data from the Millennium Cohort Study (UK) and ordinary least squares and logistic regression models to compare cognitive and behavioral outcomes, and obesity at age 5 for first-born children by maternal age at first birth. On one hand, the findings suggest that giving birth to the first child at ages 30–39 compared to ages 23–29 is positively associated with children’s cognitive and behavioral outcomes and not associated with obesity. On the other hand, delaying the first birth to ages 40 and above is not associated with children’s cognitive and behavioral outcomes and is associated with increased risk of obesity. Although the results are unable to support the argument that this occurs because of the health risks associated with giving birth at advanced maternal ages, they suggest that there is a need to more closely investigate the potential trade-offs involved when births are delayed toward older maternal ages.