They also have a an outdoor skatepark, so bring along the boards/scooters if the kids are into that stuff too. They sometimes try to keep bikes out when skate camp is going on, but pretty sure that's all done for the season now.
Most of the trails are pretty tame; you guys can have a good time exploring around the valley and up off lower Livermore Rd. Livermore is also a really mellow way down if you take the lift up for a run (you get one free lift ride if you're renting a room in the Valley). Top part is a little rocky, but my son had no problem w/ it when he was 4. Really pretty up there too.