How much time do you have? Will kids be bored out of their minds with two automobile torture days? All mentioned above are great, but they are old enough for the Griffith Observatory. Check out the interactive display inside the planetarium. If not just the view of LA is great. If you want to get to the highest point of the city, take a walk on the paved trail up to Mt Hollywood. Its about 15 min walk. Lean your back up against the entrance to the observatory and you will see the trail straight ahead. You can't get lost.
The Long Beach Aquarium is worth a visit. Kids will love it, or go down to San Diego to the Scrips. San Diego Zoo is a great place, but the Calgary Zoo is pretty dang good too, so you may or may not want to burn a day there. There's always Sea World down in San Diego.
Rents bikes and ride along the boardwalk in and around Newport, or Corona Del Mar. Plenty of places to see and eat at Corona DEl Mar. Hey, the women are sure trim and fit there so there's someone for you too
Rent Kayaks at the back bay for 15 bucks an hour, paddle up and down there for a couple hours, enjoy the ocean, no waves and its normally 4-5' deep. Pull up to one of the small beaches and hang out for a bit. If you decide to do that, I can get you more info. My kids and I do it from April through October or November. Weather is really nice this time of the year.
Get a Harbor dinner cruise. Enjoy the ocean. That's what I do with my relatives when they visit from Calgary. If not, have dinner outside on the boardwalk. Its nice and warm but do bring a long sleeve shirt as the weather can get a few degrees cooler early evenings. 68 degrees or so in the early evening is the norm this time of the year, so not a real big deal.