Where would you go? DH and I love the lakes, but I think the walks we used to do might be a bit beyond the dc(3+5).
Ds1 can manage 7 or 8 miles, but ds2 probably only about 5, with lots of breaks/food and interesting things to look at/do.
I think they'd have more fun if they were walking to somewhere to do something, rather than for the sake of it.
I was thinking about the Peaks, but any thoughts welcomed...we live in London, so ideally not right at the other end of the country.