In reply to Wilks38:
I went to Harborough Rocks the other week with my 5 and 3 year olds. They loved it because the pocketed limestone was so easy to use. 3 yo got up her first mod and diff and loved it. However, three climbs was enough for them.
If using a rope, waiting around can be boring for them, so repeating a top-rope can save faff time. Sitting around eating snacks seems to be an important part of it all, so warm weather helps if you want to make a day of it all. When we last went to Burbage valley, finding and exploring caves and finding novel ways to get to the top of the crag were all important fun features.
I have usually not bothered with a pad because they don't want to jump off. If you have two adults, one could perhaps child -watch while the other can climb without worrying about kids underneath. Otherwise, i think that focusing on the kids having fun is the priority.
Also, cars to roll off slopes, dolls for which to make dens in cracks or caves.
Just a few thoughts