How tall? (Image: Photofusion Picture Library/Alamy)

Ever noticed how a youngest child is often babied? Well, don’t blame the parents, they could be under the “baby illusion”, where the youngest child is perceived as shorter than they really are.

Jordy Kaufman and colleagues from Swinburne University in Melbourne, Australia, asked 77 mothers to mark on a wall how tall their children were. The mums underestimated the height of their youngest child by 7.5 centimetres on average, but were almost spot on for the height of any older children.

Birth order is thought to affect many things, including how dominant or risk-averse you are.


If mothers, and potentially fathers, see their youngest as shorter than they really are, they may treat them differently to elder siblings, which may be one reason we see birth order differences, says Kaufman. “One of the great mysteries of child development is birth order effects,” says Andrew Whitehouse at the University of Western Australian in Perth. “Perhaps we tend to see our youngest child as the baby and that never changes.”

It’s a striking example of a much broader phenomenon too, Whitehouse says: “How we perceive the world is different to the way the world really is.”

Journal reference: Current Biology, DOI: 10.1016/j.cub.2013.10.072

This article appeared in print under the headline “Youngest child a baby in mum’s eye”