I've only been to Cabo (that was in October) and did a beach day on our own with our 2 and 5 year old. Cabo is super easy to get around. You tender into the marina and there are a ton of water taxis waiting to take you anywhere. We hired one to take us on a mini tour of the surrounding area to see the arch, watch sea lions, and fish in the water and then around to some beaches. The water taxis can literally just run aground on the beach and drop you off/pick you up. We ended up at Medano Beach which has a lot of bars/restaurants. If you eat/drink at them you can use their tables, umbrellas, etc. (we didn't). The sand at Medano is fine and the water is warm. Our kids loved it. My only complaint is there's somewhat of a party atmosphere there (the bars play loud music with DJs, etc.). The kids didn't notice but it wasn't very peaceful for my wife and me. If I go again, I'll probably have the water drop me off at Lover's Beach (don't worry about the name -- it's fine for kids). It's much more secluded but I don't think there are any facilities like bathrooms there.
I wasn't sure what to expect about Cabo with the kids and found it the easiest port with kids. The water taxis make it so easy to get around and the kids had a blast. If you do go for the water taxis, definitely try to negotiate the price with them and I wouldn't recommend booking a return trip (or at least paying ahead for it). There are generally so many taxis (at least to Medano Beach) that you can just hop on whatever one is there to get a ride back to the marina.
Enjoy!