From Ramblers Worldwide Holidays, the tour operator affiliated with the Ramblers' Association -- they do holidays which look good but it's hard to get an impression of what they are really like.
We used to do walking holidays (the walk-from-place-to-place-while-we-carry-your-baggage kind and the guided walking kind) pre-children, and would like to find something vaguely similar but child-friendly.