Explaining the baby illusion

Credit: © Melking / Fotolia.

When a new baby enters the family, parents often report that their older children suddenly seem much larger than they had just the previous day. There are three possibilities for this phenomenon: the kids really did grow overnight, the kids suddenly look huge because they’re being compared to a newborn baby, or something else is going on.

Jordy Kaufman and others from Swinburne University of Technology are going with ‘something else’. They contend that parents view their children through the ‘baby illusion’ until a new arrival comes along and shakes them out of it.

The researchers asked 747 moms of 2-6 year old children to estimate their kids’ heights by placing a mark on a blank wall. If the child had any younger siblings, the mothers were pretty accurate. However, if the child was the youngest in the family, the moms consistently underestimated his height, and by a considerable amount. They were off by an average of 7.5 cm (3 inches).

Current Biology : CB, 23 (24) DOI: 10.1016/j.cub.2013.10.071.

It didn’t matter how many siblings the children had or how old they or their siblings were, only whether they were the youngest. As long as a child had at least one younger sibling, the mothers had a realistic impression of that child’s size. 

This suggests that parents see their youngest children as unrealistically small or immature. This illusion could entice parents to provide extra care for their youngest child, whom they perceive as being smaller and more dependent than he really is. By the same token, once they have a newborn, the illusion is broken for the next youngest kid, who, for better or worse, is now going to get less attention anyway.

It’s as if having a new baby snaps parents out of the dreamlike perceptions they had of their hitherto youngest child. I wonder how whether this baby illusion continues to color the feelings of parents for their adult youngest children.



Jordy Kaufman, Joanne C. Tarasuik, Leila Dafner, Judy Russell, Sandra Marshall, & Denny Meyer (2013). Parental misperception of youngest child size Current Biology : CB, 23 (24) DOI: 10.1016/j.cub.2013.10.071.