There is an inverse association between income per adult and fertility among countries, and
across households this inverse association is also often observed. Many studies find fertility is
lower among better educated women and is often higher among women whose families own
more land and assets. What do we know about the social consequences of events and policies
that change fertility, if they are independent of parent preferences for children or the economic
conditions which account for much of the variation in parent lifetime fertility? These effects of
exogenous fertility change on the health and welfare of children can are assessed from Kenyan
household survey data by analysis of the consequences of twins, and the effect of avoiding
unanticipated fertility appears to have a larger beneficial effect on the body mass index or health
status of children in the family than would be expected due to variation in fertility which is
accounted for by parent education and household land.