Let me also add:
Shopping: tons to do in LA area. Lots of malls, mainly outdoors ones. I recommend shopping at the Irvine Spectrum mall in Irvine - it is literally CRAZY there! The stores in that mall stays open ridiculously late - I ate dinner late one night there at at 2 AM during the weekend, the mall was still BUSTLING and the stores were still open. MADNESS!!! Ironically there are also things for your 4 yo there, as there is a ferris wheel and perhaps other fun activities. Most malls here have cinema complexes in them so you can knock down a movie as well if desired.
Sea World is great but in my opinion it gets boring after seeing the animals do their tricks. I personally enjoy the San Diego Zoo more (and it's one of the best zoos in the state). Your kid will enjoy both - your baby's mama will also have fun.
If you are driving, the drive will be a blast granted you take Highway 1 - it travels along the coast and if you depart LA and travel along the coastal highway you will pass through some of the most beautiful places in CA, including the beach cities such as Malibu (home to many many celebrities), Orange County, etc. Some beaches are insane like Newport and Huntington - they are literally jam-packed given our current weather/season. But, of course, I bet all of the beaches don't even come close to what you get at Hawaii. You will be laughing at the white caps we get and our pitiful 3-feet waves.
EDIT: Agreed with the above posters - the fireworks show in the end at night is a MUST-SEE thing! I thought Fantasmic was great! Even if they just shoot fireworks it's quite a wonderful experience as the fireworks are synchronized to nice, classical music.
I'm sorry about my outlandish behavior - there's too much blood in my alcohol system.