In reply to Mango-Bob:
Very Much depends on the age (size) rather than ability.
As Offwidth says Windgather is great for Kids. It's where I took my 5 yr old first time round. Short easy walk-in with a nice flat grassed area back from the crag where you can picnic without fear of a belay plate coming down on your head. Also as Offwidth says, I found NO issues with belays at the top - -loads to choose from.
Harborough will also work. Granted it's not as picturesque as Windgather but the bubbly pocketed rock means that there are more holds for little hands than on normal grit.
Birchen is rubbish for little kids as the crux of most of the routes is getting off the floor. The fun factor for both kids and parents diminishes if you have to start hauling straight away. How is that fun climbing.
Higgar Tor is actually really good. Loads and loads of 'weaseling' to be done and quite a few short buttresses that are easy if you are 5'10" but a fun challenge if you are 2' 6"!
Burbage North (Ash Tree Wall Area) works as well.
Lawrencefield Roadside Bay has a couple of good easy routes plus a great abseil.
The main thing to remember is that if you are wanting to take the child climbing again, don't overload them at the start. Fun not quantity!!!