In reply to jogwen:
I think a lot depends on how determined you are and how much you are willing to carry. We have taken our wee man (not so wee now - 8) to a lot of places over the years from the start - I think the first trip was a few weeks old. Most Peak crags are suitable, Stanage, Lawrencehill, etc and in the Lakes there a hundreds of single pitch crags suitable. Same for Scotland, as long as you have somebody supervising the child whilst you are climbing, you can almost go anywhere weather permitting including mountain crags. A lot of the Scottish crags are very suitable as they are not busy and often have water/ streams/ bog etc to play in. ) Another tip wellies!
I can recommend a pop up sun/windshelter tent from Quechua (which we were given as a birth present) and has come with us everywhere and is still in use today - we can all shelter there if it rains.... It's invaluable. They still sell it in Decathlon for about 17 pounds or so).
Post edited at 12:54