The postponement of motherhood is one of the most important trends in fertility behaviour in the last few decades. The consequences of late motherhood for child health are not well understood, however. One reason is that in the study of child health, the focus is either on birth (e.g., risk factors for low birth weight), or on child health after birth (e.g., child health consequences of low birth weight). The comprehensive view to child health underlying this paper is that both sides are closely linked. Those perinatal, behavioural and socio-demographic factors which affect birth weight also affect child health after birth. This paper addresses both issues together on the basis of two sets of Belgian regional data. The focus is on the relation between maternal age on the one hand, and birth weight and weight gain after birth (the latter conceptualised in an innovative way) as proxies of child health on the other hand. Our results confirm the importance of high maternal age as a risk factor for low birth weight. They also point to a long-term, though not necessarily permanent, effect of high maternal age on child health after birth for low birth weight children. These results differ from those of studies using other proxies for child health after birth such as physical and cognitive development, which point to permanent negative health effects of low birth weight, and even raise the question of negative intergenerational fertility effects.