If you're camping then I'd go for Park Foot campsite near Pooley Bridge.
It's a good family campsite ( not cheap though ) but plenty of facilities to keep the whole family happy such as park, resteraunt, bar, tennis courts, take away food. Plenty of fields too - some right next to Ullswater.
There are some easy walks nearby - get in the car and you'll soon be at Patterdale, Helvellyn, Blencathra Aira Force waterfall, etc. There's a couple of castles close by as well as one or two stone circles.
When our kids were young we stayed there a lot as they could have the run of the place without too much supervision.