It's hard to say if a 5 year old is a boy or girl withought clothing identifiers so it's not always obvious. However, from a practical standpoint a dress takes less effort to make, you don't outgrow them as fast, and it makes changing faster so I can see why it would be the gender neutral choice.
But why does it need to be obvious? Traditionally sexism led to people liking to flout their boys, but today I would hope we would be passed this (albeit pie in the sky thinking, we obviously aren't past whats in a kids nethers).
I can't wait for the day people just don't give a crap if the 5 year old has a dick or not.
'They' is fine as a singular, for instance the person that you have just replied to, they say that you are completely wrong, and I agree with them. See?
That's pretty cool. The verb conjugation for "to be" seems to be actually useful in this context. It sounds a little wrong to me, but that's just a matter of habit, and it would probably flow better in written English than writing he/she.
You're in dangerous territory if you ask boy or girl - people often assume their child's gender is as obvious to you as it is to them. I've gotten some unexpected hostility from strangers this way.
I don't know about potty training. Disposable nappies are a miracle of habituation. It seems they can deposit bucket loads in them and never know it - at least until they saturate and the dam bursts.
Living in a climate that is warm to hot most of the year, little kids basically just need a nappy and a tshirt or singlet around the house. It looks very ghetto but it is practical and not unlike wearing a dress I guess.
Chucking shorts on over the nappy to dress up for a public outing doesn't seem to alter the complexity of things appreciably. Little boy fire engines take great pride in being accessorised with a fire hose and whipping it out never seems to present any challenges or inhibitions to them. At least compared with aiming it. Perhaps we should paint a fly in the toilet bowl.