Oh we all climbed trees as boys but going up mountains is not really climbing it is walking. Unless you need equipment or do it like Sundog´s guy.
When I was a kid we used to go up mountains every weekend in Llanddulas North Wales, Maiden´s Leap for play along the edge of the precipice on Saturday and Clipturven for the Sunday walk.
Wales' mountains aren't high but they're steep. It might not be Climbing with pitons but it ain't walking.