Unless your kids are pretty good tech and fit I wouldn’t recommend it. If you have to go there, then fine, make the most of it, but if you have the option of another TC then I’d take it.
The problem with Grisedale is that there are no flattish routes. Even the beginner trail has some hefty hills on it. I seem to recall there being a sign at the top of one downhill suggesting cyclists dismount or something.
So given that all the routes we found are hilly, you might as well go for the one with some decent singletrack. I think most of the beginner routes are all tedious fire roads. Which leaves you with the North Face Trail.
We’ve done the TNF a few times with our kids, since the youngest was about 6 with huge amounts of assistance. But it’s not ideal. I think the big one was 8 before he rode nearly all of it. Normally I tow the wean up the biggest hills at trail centres, but the TNF starts with some really gnadgery techie uphill singletrack which you obviously can’t tow on. It’s a lovely piece of trail but a 7 year old would need to be pretty good and pretty fit to enjoy it.
There is a detour option marked on the OS maps past it, but I’ve never managed to find it. So we always do the singletrack uphill and the wean always moans about it. He loves the rest of the route, but the first bit is just too hard for him. (he can do the Freeride northshore at Llandegla as a reference point).