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Being the littlest may mean more protection and care from parents, psychologists say.
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If you're a youngest child, your mother may call you "the baby," even if you're 6-foot-3. It can be endearing or annoying, depending on how you're feeling about dear old Mom.
But, it turns out, lots of parents think their youngest children are smaller than they really are, Australian researchers have found.
When they asked mothers to mark the height of their youngest child on a wall, they consistently marked it lower than the child's height. And not just by a little bit.
The moms thought the baby of the family was three inches shorter than in real life, on average. For children 2 to 6 years, old, that's a big difference. For a 4-year-old boy, knocking 3 inches off his 40-inch height means his mom thinks he's barely as tall as a 3-year-old. (I checked the Centers for Disease Control and Prevention's children's growth charts for the comparison.)
Mothers had no problem correctly guessing the height of their older children, the researchers found. On average, the moms were off by only about one-sixth of an inch.
Psychologists at the Swinburne University of Technology in Melbourne, Australia, came upon this discrepancy after an online survey of 747 mothers found that after they had a new baby, 70 percent said their second-youngest child suddenly looked much bigger.
Well sure, the scientists thought, that newborns are pretty small by comparison.
But third-youngest children didn't get a sudden boost in perceived height when a new baby entered the family, the researchers found.
So they decided to look further. They recruited 77 mothers with at least one child between the ages of 2 and 7 to do the mark-the-height-on-the-wall test.
The older the youngest child was, the more likely that the mother would underestimate her or his height. Overall, the mothers consistently estimated that their youngest children were significantly shorter than the mean height for children that age. It was almost as if the moms were pushing their hands down on top of the kids' heads, saying, "Stop growing!"
The results were published in the journal Current Biology.
This "baby illusion" may be the flip side of the concept that baby humans (and animals) have cute physical features like big heads, round faces and wide eyes so that adults will be more likely to protect them and care for them.
In this case, parents are giving babyish attributes to a child who may no longer be a baby.
And it may reflect the influence of that oft-heard wish: "If only they'd just stay little."