Sunday evening drives can be LOOONG. It can take up to 2-3 hours to get back up to LA.
As to how long to visit Legoland, it depends on the ages of your children and how much they love Legos. When our son was younger, we did 2 days. Now that he's older, we can get through with 1 day. They've opened 2 new *lands* since our last visit, so I'm budging 2 days, especially since the park is only opened from 10-5, or 10-6 next week.
I would think if the park closes at 5 or 6, have dinner at the Carlsbad Outlet Mall or somewhere around there. You don't want to be driving north on the 5 on Sunday. Ruby's has great food, as well as San Sai, Claim Jumper, and lots of other places that are good for kids.
I would say one day for Legoland. There are a lot of little kid rides that the 6yo might want to skip. And the 17yo might be bored...I was my first time. It's really not a big park, and only a few bigger rides.
we did legoland in one day, we were there at 10:15 a.m. and left at 4:30 p.m. We had plenty of time to do everything...however note we went in extremely "off season".
For what it's worth, Anaheim is a lot closer to Legoland than LA. I can see it taking up to 2 hours with bad traffic, but 3 hours would be unusual without a specific problem like a multiple-lane accident. The traffic from San Diego can be really bad on Sunday evenings, but the freeways have been much better here in Southern Cal. the last few months with these crazy gas prices. If I were a betting man, I'd put my money on 1-1/2 hours from Legoland to Disneyland leaving at 6pm on a Sunday evening right now.
I asked this in another thread about driving to San Diego but I thought I would try here too. I am so torn on what days to do Legoland based on drive-time and crowd levels. We are staying at Best Western Park Place Inn across from Disneyland for a week at the end of June and two of those days we will be doing Legoland (as long as we find a reason to go back on a second day). Should I make those days on the weekend or a weekday? Or one of each. I would prefer to avoid the larger crowds and was considering weekday (Friday and Monday) visits but now I'm concerned about traffic. Anyone know which would be better? Our family is myself, my wife, 3 boys - 8,6,4 and a daughter 1 1/2. I think the boys will just love it and we'll definitely need both days.
We went on a Wednesday and had no traffic on the way there and minimal traffic on the way home. We hit it about 4 miles from DL. We stayed at DLH and rented a car from DTD Alamo and it worked out great. I think I would steer away from a Friday.