My personal opinion is that excluding kids really isn't the answer here (I don't really know what it). I started here when I was 13 and it probably took me 2 years to start churning anything semi decent - I mean, they weren't really educational and they certainly don't have any technical merit, but I think they provided entertainment to a few people and I had a lot of fun making with and experimenting with things I'd seen here and making my own scenes using tech demos. I agree that price is quite possibly the reason for a lot more kids getting involved, but that shouldn't be a bad thing - I mean this tool is one of the primary reasons I've applied to study engineering at university - even if I'm no longer active on it. The key really is to teach those kids how to use each and every feature of algodooo (and by limiting the iPad functionality I think the devs have created some of this, along with making it free, which is great), by providing YouTube links to tutorials and making more of some of the old scenes (expand on the featured section maybe to not only scenes that people shamelessly volunteered on the forums - which I don't think many people know of and use), make more of the forum community and really inspire these kids to make something better - rather than cutting them off by filtering everything they make out.
On another note I love how many old users have come on just to drop a note here - cue Kilinich/Paradigm/ Dare/cata/shark/Ndxt and all the rest