Our family of four had a good experience staying here and visiting the beach and Legoland. The management was very helpful and there are many items in the garage for the beach which will be useful, like a wagon and boogie boards and surfboards. I was initially cautious about the lack of AC, but the temperature really does stay magically nice for summer time.
For other families with little kids, I'll just give a couple words of caution: yes, this place is very close to the beach but the terrain in San Clemente is extremely hilly. We ended up just driving down a minute or two and using the cheap parking, which was abundant and was always available. But I wouldn't use a wagon or expect kids under 5 to walk if they're not used to it.
The other items are a) there's not really a way to block morning sunlight, and b) the loft area and the bed are one very big room at multiple levels, so sound travels.
These items didn't cause any problems for our family though. We actually got to bed early and woke up refreshed and ready for fun. And, the arrangements of the stay were super convenient. If we come back to San Clemente, I would stay here again!