At the far end of San Diego, at the far end of Point Park, is the best view of the area. The Cabrillo National Monument is part of the National Park Service and is absolutely the best view of the area. I could sit up there for hours just watching the boats go by. You have full view of the sub station, the Navy base, and the city of San Diego. They have a small museum, a gift shop with really nice stuff in it and an "oh my!" view of the area.
There is plenty of room for kids to run around, but they probably won't appreciate the view and the history as much. If you have a National Park stamp book, you can get another stamp in it. Oh, and there is a monument. . .