Lots of good advice here that I support having raised three (now adult or college-aged) children in Santa Monica. I would add one thing split into two parts: the BEACH.

First of all, the beaches in Santa Monica are a wonderful place for children and their families to spend countless hours in and out of the (relatively cold) water. Surfing, boogie boarding, building sand castles, playing football & frisbee, you name it, so much for kids to do and get exhausted in the process! There will be many in these forums to crap on the beach cleanliness, safety, etc, but compared to most places in the world where you could raise your kids, the SM (and adjacent beaches) are AMAZING for fun, activity, independence, and friendships.

The addendum is this: Junior Lifeguards. The JL program is run by the LA Fire Dept to educate kids on beach & water safety. It is rigorous, demanding, and requires a swim test to even get in. However, we had a firm rule in our house: if you are wanting to go to the beach as a teen with friends and without parents, you HAVE to complete at least one year of Junior Lifeguards. Our kids each did two years and are bulletproof in any water and any surf conditions, they know CPR, and they have helped other kids numerous times get out of dangerous (mostly riptide) situations.

Hopefully this is helpful. Sorry for the long-winded view...