Visiting Legoland California

Do you mean Sea World, in San Diego? Legoland in north of San Diego, and both places are big with lots to see, I don't see how you could do them both in one day.
I love both parks, but if I had to choose, I'd choose Legoland, just because it's so unique, and my kids are (were, when they were younger) Lego fanatics, especially my son.

Sea Life can be done in an hour or less. It is very small. We have easily done LEGOLAND in one day, including Sea Life. Plan more time if you want to go to the water park though. There is a water area in LEGOLAND proper too.
It can be very warm during the day but get very cold in the late afternoon and evening so bring layers.
There is a severe shortage of shade. Bring a nice brimmed hat or even an umbrella. This was one of the big things that struck me when we used to have passes. We went a few times while our youngest was really young before our passes expired to let the other 2 run around and burn off steam and it was next to impossible to find somewhere to sit with shade.
Make sure you look at the website for height restrictions on rides. A lot of them have some restriction. A lot of them are 2 seaters so your family gets split up a lot. There are also a few where the child goes on by themselves while you stand and wait for them.

ETA: You mean Sea Life at LEGOLAND and not Sea World correct? If you mean Sea World, that is an entire day trip by itself.

Sea Life is a nice aquarium and you can easily get thru it in an hour. At Legoland the pirate ride is fun, but you will get wet. It's good idea to bring extra clothes. 36 inches is the height requirement and many things will not allow you to have infants sitting in your lap. Be prepared for that. Plan to get there right at opening to get both done in a day, but it's definitely doable.

If you go on a warm day, bring bathing suits or a change of clothes and a towel. There is a great water play area in the actual Legoland Park (not the separate water park) and the kids will love to run around through the water features and slides.

If they want to do the ride where they drive the cars themselves, do it early, since the lines get really long later.

If you're going before May 12, try to carve out an hour before or after you go to visit the flower fields just outside the park. They are really beautiful and fun. http://www.theflowerfields.com/

We really liked Legoland and SeaLife. They're really manageable in a day, well organized and have tons of bathrooms (unlike Disneyland, where we'd been for three days before Legoland).

We ate at a sit-down restaurant toward the back, near a roller coaster. It was great! Nice to get the break from the crowds and they had a terrific kids buffet with things like grilled cheese and hamburgers, fruit, french fries, etc. Even our super picky son loved it.

I did notice the Burger Kings have a discount for both. I can't really say what to do. When at Sea World try to make a show. Other than that, run for your lives to do as much as possible in one day! Have fun!

Both Sea World and Legoland in one day will be rough. Go to their sites and plan what to see at each, there's a lot of walking, you need a plan to stick to.

Legoland is awesome! It's my favorite park. It is very clean and they have some amazing lego structures. Check out the rides on line before you go to see which are appropriate for different age groups. There are some rides younger kids can't go on and some that are too young for older kids. Sea Life is very small and it is ok... not the best aquarium. If you miss it, you're not missing much but if your kids like aquariums it's worth a look. If you go in summer, definitely bring a bathing suit or change of clothes because they have some great water rides and they have a whole water park area and the kids will get wet. Get there early when it opens so you have the whole day. Also, we pay the extra money for the closer parking because at the end of the day you want to get to your car fast. Have fun!

Depending on when you are visiting, the water park is a real blast! I would rather split time between the park and the water park then the aquarium (granted I don't know the ages of you children).
Truthfully, you could spend a full day at Legoland and not see/experience everything ... it is a great park and I hope you have a wonderful time.

Read the fine print on the Burger King coupon. You have to buy a park hopper in order to qualify for the discount. Definitely bring a change of clothes! Food is not that great so snacks are a good idea too. The sea life aquarium was just so-so. And do NOT let the time share folks woo you into a $150 gift certificate (thankfully, we did not). Oh, and for the grown ups, I highly recommend the robotic arm ride thingy. So much fun!

What age is/are your child(ren)?

They have a ride there called Sky Cruiser that is super popular. Unless it has a very short line, skip it. Our first trip there, we spent an hour in line for that ride alone and the entire park was only open for 7 hours! Also, if your little ones are younger than 4 or 5, pay close attention to height requirements. They have height requirements for most rides that quite frankly don't need them. My 1 year old can only go on about 4 rides in the entire park.

SeaLife will take you about 30-60 minutes to go through. LegoLand is geared toward younger kids. It depends on the ages of your children, what day you go, etc. We've been mulitple times, and it is interesting, but the older your kids are, the less time it will take you to get through. The Star Wars exhibit and the Lego Villages are really neat to see. You can easily get through both parks in one day.

We have an annual pass to Disneyland, but would never dream of doing the same for Legoland. Like I said, it is interesting, but odds are, you'll never go back if your kids are over 11.