I want to take my son on a short trip this summer (saving for a house, not too much money to spend).
A few cheap ideas:
Camp out Table Mountain $15 a site.
Not as cheap; I heard you can camp out at the San Diego Wild Animal Park and San Diego Zoo. That sounded fantastic to me, but your kids have to be 4 and up. They also have an adult only wine camp out.
Join the San Diego Zoological Society and have 14mos. free Zoo and Animal Park for two and two passes for guests.
You can go online and get a camp site at the beach real cheap and it will have bathrooms and showers. I am going to San Onofre this Summer.
Go to the Getty Museum or Huntington Library. The little kids really like the Huntington.
If you use AAA or know someone that does they have a lot of great ideas and further discounts. (ie. A year for a days admission at Seaworld)
Look for hotel rooms and vacation deals on Hotel.com, orbitz, travelzoo, and travelocity.