In reply to samparsons:
Kids love them but will soon run out of climbs to do on them. The accent is therefore on short, easily-priced sessions with an emphasis on herding them through, so having a helper to speed up kit-fitting is worthwhile.
Some operators will quote you for hire of wall only, others will sell you a full package with their own instructors. One issue that is worth looking at is whether it is appropriate to have kids wearing helmets if the wall is using an autobelay system. Helmets have been known to get hooked over holds on descent, creating a strangulation possibility.