Except that's not just a belief, but results of the studies.
The fact that grown ups are different is clear (although studied as well), but there was a theory about all that being a result of society influence, so scientiest went far into early stages.
Couple of month old babies were examined: girls tended to choose humans, boys tended to choose "things".
Then there was a doubt, that, oh well, maybe those babies were already "spoiled" by the society, so someone went as far as to check one-two day old kids.
Boys were interested in things, girls in human faces. (I didn't know kids could see at that age).
Another studies: increased levels of testesteron have a very clear impact on kids development:
1) it will take longer to learn to speak
2) it will have greater interest for "things" mechanisms etc.
There are numerous studies showing that:
1) girls/women do better on average
2) boys/men are overly represented in both top and bottom parts
Which suddenly explains why Nobel laureats are mostly men, and, cough, CEOs too.