I'm guessing UK cons are more stricter on this possibly as I've never seen kids at ones in the UK, they tend to stick to 18+ only - The ones who do manage to slip in only get in unofficially by booking hotels at the same time as the con on purpose, but can't get into the actual con rooms to take part without membership. I definitely think 18+ is the safer option seeing how so many cons seem to be boozy sex festivals. Even then, a lot of the kids who sneak alongside the hotel to try join in often get older folk avoiding them like the plague.I can tell you that's not true. Rainfurrest allowed minors to attend as long as they were chaperoned. That seems to be the case with most furry conventions. We've seen plenty allow infants as well which is apparent in Khord's thread.
Anime cons here tend to be compltely open for kids too despite the nsfw being there as well, though hidden under tables.
If I recall, the whole strictness of 18+ here is mainly an insurance thing or something. But there's definitely a more adult themed environment here and interacting with kids who tailgate around is seen as a bit of a no no.