There is a lot of hiking and camping in the San Diego area. One of my favorites is the Lake Poway area which of course is near Poway, CA and just north of the city of San Diego. You can boat and fish on the lake and have a picnic in a beautiful setting like the one in this picture. The kids will love everything about this and there are many hiking trails that are family friendly. Check out the city of Poway website for further information, http://www.poway.org/Index.aspx?page=638. Even if you are camping somewhere else in San Diego Lake Poway is worth a day trip.
Maybe you can even set a record for catching the largest fish here. On the website you can check out the current records for the different types of fish and the record.
Another great place near San Diego is Palomar Mountain State Park. You can get all the information about this park by visiting http://www.parks.ca.gov/?page_id=637. The scenery is beautiful and so is the view up there. It will snow in the winter so I think it is best to avoid camping there then. But if you live near Palomar Mountain it is a great place to take the kids when it snows for sledding.
When I have taken my kids there we usually see deer and lots of wildlife. Also there are beautiful flowers in the spring when the weather starts to warm. It’s just a great place for an outdoor family day or for overnight camping.