Have a kid's day at your club's range. Run an ad in the paper and invite parents to bring their kids out to the range on some weekend. Try to have a bunch of kiddie bows and a whole bunch of arrows available. Get as many volunteers from your club as you can to help the kids with their shooting and to supervise them. At least one volunteer for every two kids on the line is good.
Maybe hire a party clown to entertain the kids while they're waiting their turn to shoot. Or, maybe, have someone there doing demonstrations on making a selfbow, or making strings and arrows. If you've got a leatherworker, have him set up and make some armguards and tabs or something like that. Parents would be interested in watching those kinds of things too and, trust me, you don't want parents just dropping the kids off and leaving. So you need to have something to interest them as well.
In fact, it wouldn't be a bad idea to have some lightweight adult bows for the parents to play with too.
Get several bigbags of cheap balloons. Blow them up and pin them to the targets for the kids to shoot at. It'll make a mess on your practice range, but kids just love popping balloons with arrows. They'll get bored pretty quick if they're just shooting at paper targets but they never get tired of seeing the immediate results of a hit on a balloon.
We've done that several times at our club and always had a great time. Nothing like watching kids having a ball.