In reply to ceejasix:
There aren't many child friendly venues that come to (my) mind, first would be the lower tier of Dancing Ledges. The approach is easy enough but you'll need to keep a tight grip as there are plenty of vertical drops. The routes are all top ropeable, holes have been drilled at the top rather than the usual stakes or lower offs. You can thread slings and top rope from below like you would at the climbing wall.
The other place known for child friendly climbing is Godnor on Portland. However these routes are steep and I think they need an adult to climb/lower off the anchors at the top which might give logistical problems if you don't have a climbing partner with you. The Cuttings has some easier routes but again the anchors need to be clipped from below.
And there is a big slab fallen block somewhere on Portland down by the sea but I haven't been there myself.
Eager to hear of any other venues (my son is 10) that others can recommend.