Francis Bay
Francis Bay is home to one of the best all around beaches on St. John. It's a very large, sandy beach on the north side of the island that is calmer than many of the other beaches. The swimming area is surrounded by bouys, which combined with the calm sea makes for a great location for children.
The beach is often not very crowded, and even when there are people there it is large enough that it doesn't feel crowded. There are picnic tables available to each lunch or snacks on, and even grills in case you want to cook your meal. There are also public bathrooms and garbage cans available for use.
Francis Bay offers many different possibilities to snorkelers. The calm waters of the bay make it a favorite spot for fry, which is a site all it's own. Thousands and thousands of tiny fish swimming in huge clouds. But of course the presence of the fry draws many other large fish the scene as well. All of the usual suspects for St. John can be seen here such as barracuda, parrotfish, angels, turtles, rays, and many more. Of course there's also rich coral growth and plenty of other invertebrates to enjoy.
Areas of sea grass and the rocks on the south end of the shore offer shallower, easier snorkeling with lots to see. Deeper water and the other reefs will contain even more exciting animals, but may be a little more challenging for those that aren't the best swimmers.