With the birth of a new child many parents see their previous child as having suddenly grown. It was thought that this was because the comparison with a newborn baby made even a small child appear very big. A recent study asked seven hundred mothers with children aged 2-6 years to mark on a wall their last child’s height as well as that of their first child without actually measuring their children. On average the height of the last child was 7.5 cm less than true height whereas that of the first child was roughly correct. Parents usually see their smallest child as smaller than what he/she is. For each new child that comes into the family the preceding one is now seen correctly and therefore appears to have grown. In the distant past having many children was a way of guaranteeing continuity of our species but inevitably these children were all rather close in age and could be confused with one another. However, seeing the last one as much smaller helped the mother easily identify him/her in the group and so give the attention and resources that older siblings might have wanted for themselves.