The OP never really said what they believed constituted being "clocked" by children. Or how young. If it's simply being stared at without an accompanying "mommy, why is that man in a dress" then there's no indication they've worked anything out. Anyway, kids categorise things in weird ways based on the only evidence to hand - for example, a neighbour's 8 year old daughter once presumed I was older than her father because I was taller than him (I wasn't older, it was based on the presumption that as you get older as a kid you grow taller, ergo really tall people must be quite old indeed!). It was an odd piece of logic but made me remember how I used to put 1 and 1 together to get 11... I mean, why not? When it comes to gender, it's one of the key differentiations children learn at an early age, including what is considered "correct" clothing, look and behaviour for men and women. Kids don't have a filter to stop them from asking embarrassing question out loud when things don't add up the way they think they should.