Newlands was going to be a suggestion of mine.
I'll go for this one instead.
Helm Crag, Gibson Knot, Calf Crag, Steel Fell from and back to Grasmere. You don't have to climb the howitzer on the top of Helm Crag if you or they don't fancy it, Wainwright never did. It's not too far and you need to do the descent from Steel Fell while your knees are young.