Did you notice how your grandchild loves water? They tend to love pools and the ocean because it has a relaxing effect. Some of the children might wander off and a neighbor will find them in their pool.
Make sure that you teach them not to go into the water without an adult around. Secure all pool areas. As you teach them to swim, you will notice, that they might love the activity for months or years, and then suddenly refuse to do it. Do not push them to do it, just offer and then they will eventually go back to swimming and jumping into the water.