Just intrigued me as I keep asking my toddler if he's having a brother or a sister (now 28wks but haven't had sex confirmed) and DS has until recently said a sister (but now saying brother 
)... My friend recently went for a scan and the sonographer asked her if she'd told her two boys (one 3yo) and she said yes, that the 3yo had been v interested in her tummy/boobs before she'd even given them the news and says he is having a sister now they've discussed. Sonographer said this is common and that toddlers (up to 5yo) are usually able to tell you if you are having a boy or a girl!
Would love your anecdotes on this!