I actually don't know how many kids there are in the opera house. To the best of my knowledge it's at the discretion of the RPers to play children, and they are all god-modded by the parents -- that is to say, character's children are treated as NPC (non player characters) and are generally kinda like props. Their actions and any words are dictated or described by the ones who are RPing their creators. If they're at a certain age, as of yet undetermined, but talking walking and forming thoughts that could be posted in general, an official profile should be set up and they should be treated as a legitimate character -- but a child under five, say, could not realistically be played as a character. I think Hollie had a character in the single digits once, Cassander, which worked for her. We can definitely start a moderator discussion and create rules for these instances if we are seeing a need for it.
There are complications that come along with role playing children in general; staying in character within the limits of the age, for instance. Also if your child character was older and being played in tandem with your other characters, you could not for example have a scene between Jean and Polaris (father and son) and another character because of the Character Guidelines
and RP Guidelines
. There would be no point. It would be RPing with yourself, and most likely double posting, which is not allowed.
Hopefully this is answering some RP questions for you, if it's not clear keep asking questions. :)
If you just want to set up "play-dates" with other RP parents, then by all means mention it in the OOC Thread