How older children interact with their siblings is tied to the younger children's development, Canadian researchers found.
"The idea is that here is this effect of being in a large family where you don't get that many resources, but if you get an older sibling that's really attuned to your needs that would be a modifying effect," Jennifer Jenkins told Reuters Health.
Jenkins is the study's senior author and the Atkinson Chair of Early Child Development and Education at the University of Toronto.
Previous research had found that children from large families tend to score lower on vocabulary, IQ and other academic tests, compared to those from smaller families.
"That's been pretty well examined that the larger the family, the less good the child's skill in language and IQ," Jenkins said. "It's really thought of as a resource dilution."
For example, if a couple has a second child, the attention they spent on their first child will then be split among both kids.
She cautioned that whatever effect a large family may have on a child is small, however.
To see whether an older sibling can possibly fill in for some of that diluted attention, the researchers used data from an existing trial that included families from Toronto with 385 young children who had a sibling at least four years older.
Mothers and older siblings were scored on how they interacted with the younger child.
For example, the researchers scored whether the older sibling or mother were sensitive to the younger sibling's abilities and gave positive feedback.
The younger sibling's vocabulary was also tested by having the child point to an object's picture after its named was said out loud.
The researchers found that children with many siblings tended to score lower on the vocabulary test, compared to those who had smaller families.
Children from large families whose older siblings scored higher during the interaction, however, tended to score higher on the test than those whose older brother or sister scored lower during the interaction.
The association between an older sibling's so-called cognitive sensitivity and the younger child's score remained strong even when the researchers also accounted for traits that might have influenced the results, such as gender and age.
While the overall association may be small, Jenkins said many traits that are associated with similar cognitive delays are of a similar size.
"It's multiple and multiple accumulating influences," she said. "I think all of these small influences are worth paying attention to."
Image: Siblings, via Shutterstock