I can't think of any campsites around there, and I walk in that area quite a lot. I know of people who have camped near the pub in Hesket-new-Market, the Crown, in a semi-official way. It might be worth ringing the pub to ask about this. Another option would be to stay at Skiddaw House, which is an independent hostel affiliated to the YHA. Great location and run by a very friendly couple.
My son now likes hill walking for its own sake, but used to grumble a fair bit unless there were distractions and challenges along the way. Streams to play in fell into the former category, and rocky scrambles the latter.
We went on a walk the other day with some friends whose daughter is younger than my son and apparently isn't normally keen on just going up a hill or hills. My son and his pal chose the route, which involved slogging up a fell through waist deep (for me) bracken, and the little girl really enjoyed it. I suppose it was a real adventure for her, like being in a jungle, and the hard work didn't bother her at all.
It's a nice biking pack, but you're asking a lot given you can buy it for about the same on-line, with the advantage of being able to return it and having a "contract" with the retailer should anything go wrong. Just sayin.