we're just back from Whitecliff Bay this evening! - are you camping as in tents? If so, then you're across a road from the evening entertainment/bars/swimming pool, there's not anything at this time of year for kids per se, but it's directly above a sandy beach with rock pools and fossils and cliffs to climb etc etc. I beleive there is a kids club thing in the summer, but we've only been there end April/early May.
We were staying there as part of a sports thing, but we'd consider it for a family holiday (DDs 5,9, and 14) - it's a pretty good base to do stuff on the island.