If the children are supervised by a parent or other family member, no crb check will be needed. Otherwise, a crb check is cheap and really easy to do, but will have to be initiated by the club, rather than individuals involved. It isn't too hard to have one for a couple of members who can run the sessions. I don't know why people have to over inflate the difficulty of filling a form in and sending £30 or so, for the benefit of ensuring the worst amongst us do not prey on children with impunity, but there you go.
Much more important, a safeguarding policy should be written up. An evening of work at most. The bbka will have one so you could copy theirs, or phone the council and they will have a designated safeguarding team who will be able to advise on writing one (they probably have model policies on their website) The nspcc also have examples online, so cut and-paste should take ten minutes.) if you have safeguarding procedures that people can follow, parents can be confident their children are safe and catered for.
I have taken an observation hive into schools without crb checks. If teachers are present at all times there is no need for one. Even if they insist on one, it is no admin for the beekeeper, as the school will do it all.
Sorry to go on, I get a bit miffed when people exaggerate the difficulties of involving children safely.
The other things I would add: Make child specific welcome packs, rather than sending them the same versions as the adults. Have children only groups, so they are not intimidated by adults. Keep things interactive rather than passive. Ie, workshops in the day rather than talks in the evening. Even for teenagers, a specific group might be helpful, as they'll enjoy socialising together.
