Mental Health

Youngest Sibling Perceived as 3 Inches Shorter Than Actual Height

By Christine Hsu | Update Date: Dec 16, 2013 12:30 PM EST

New research may reveal more reasons why younger siblings get "babied". Previous studies show that firstborn children suddenly appear taller when their younger siblings are born.  However, a new study found that until the birth of the new child, the youngest child in the family are subject to a "baby illusion" because they are routinely misperceived by their mothers as being smaller and younger than they really are.

"Contrary to what many may think, this isn't happening just because the older child just looks so big compared to a baby," Jordy Kaufman of Swinburne University of Technology in Australia said in a news release. "It actually happens because all along the parents were under an illusion that their first child was smaller than he or she really was. When the new baby is born, the spell is broken and parents now see their older child as he or she really is."

Kaufman and his team asked 747 mothers and found that 70 percent of mothers "felt" a sudden growth in their firstborn's size after the birth of a new infant.

Afterwards, researchers asked mothers to estimate the height of one of their young children by drawing on a blank wall. The findings revealed that mothers significantly underestimated the height of their youngest child by 7.5 cm on average. However, height estimates for the oldest child were almost accurate.

"The key implication is that we may treat our youngest children as if they are actually younger than they really are," said Kaufman. "In other words, our research potentially explains why the 'baby of the family' never outgrows that label. To the parents, the baby of the family may always be 'the baby.'"

"We cannot trust the accuracy of our perceptions," Kaufman added. "In this case, it shows that our feelings and knowledge of our children affect how we actually perceive them. But it's important to consider that this misperception may actually make it easier to quickly distinguish one's youngest child from the other children."

The findings are published in the journal Current Biology.

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