Playing as a child in Exalted is a possibility left in the book, even though it's not a very optimized one (I know, I looked). And, roleplaying-wise, it's actually pretty hard to do in a convincing manner. It's brave to even try it.
I had to whip out a Really 700 Years Old the only time I wanted to play a kid, and in Exalted, that's pretty par for the course. As far as I remember, Solars don't exactly age once they've ascended, isn't? In my book, you don't need much more, it's actually a good way to explore new kind of roleplay.
In all seriousness, tough, unless you play with very immature players, the "problems" shouldn't even be part of the question. Seriously. Point that to the people who bring that question. And even if they're concerned about child abuse in a more wide spectrum (even just getting hurt and made prisoner or so), you're a freaking Player Character, that's the kind of thing no-one would bat an eye on if you were five years older!
They don't have to, but like I said, it serves as a handy excuse if someone else tries something. Usually, you at a bare minimum need to roll extra dice against a social attack if the orientation is incompatible, but the game tends to act as if ace=straight, so the extra dice to ward it off doesn't exist. If I play a child character, it usually keeps other characters from even trying anything, so whether or not I have extra dice to resist doesn't matter.

I think my hunt for an online system just came to an end for a... relatively odd reason. I have an idea for a really great character that I'd like to play in an Exalted series. Problem: said character is a child (ish). That is banned on most online R Ps due to the risks that now appear to be a little obvious. Here's the thing: I actually tend to prefer to play child characters because I'm ace. I'm awful at roleplaying anything sexual in nature, so having the excuse that said character is in fact a child and thus isn't interested in that sort of thing is very useful to me. Oh, the Irony. Unfortunately, the character's backstory is built around a combination of Parental Abandonment and Not Growing Up Sucks (with a general theme of family), so I'm... stuck. I guess maybe this is a kinda weird problem to have, but my in-person roleplaying groups keep crashing around me, so I'd like to be able to try an online one in order to avoid that. ...Would it be really obnoxious of me to explain to one of the people running the forum my perfectly innocent logic?