When we went with our kid in December (ages 3, 6, 9) we brought along a blow up raft/small boat type of thing. It had a little rope attached to the front so we could pull it along with us. We just took it out with us when we went snorkeling and the kids had something to hold onto (or get into) when they were tired or if they needed to adjust their mask/snorkel, etc. It wasn't too much trouble for us to hang onto the rope while we snorkeled and the kids were more willing to venture out knowing that they had somewhere to rest. This was especially helpful when we went on our own to St. John, since we didn't have snorkel vests.