You will find everything that will make children happy: low tides, green grass, sand, water, rocks, squirrels, and if you walk towards San Francisco, you will find a little museum called Crab Cove. It is free and you will find information about the bay.
It's a perfect beach experience close to home. When the tide goes out the kids can walk far out in the water and look for sea life. The water is nice and the beach is clean. They have a really fun Sandcastle Contest every year in June that we never miss. It's a wonderful community event and some of the castles/sculptures are amazing. I
Alameda has two main beaches Alameda Beach and Crown Memorial State Beach. Both have their charms. We like to spend time at Crab Cove at Crown Memorial. This is a great "baby beach". Meaning - small enough to let kids run free and calm, warm water. There is a big grass field adjacent to the water for frisbee and plenty of bbq pits to get your grill on. On top of all of this there is even a small, free aquarium that has a few tanks of fish, some fossils to look at through magnifying glasses and even a gift shop.