It is very possible that an adult would get rattled when a kid would ask what is water made of. One can go on a lengthy explanation of the composition of water and that it is a covalent of two hydrogen atoms and an oxygen atom. That would launch another set of questions for sure. Maybe one would have an easier task by telling the kid that water has three different states. It can be liquid in the worm of water that people drinks. It can also be solid like when it freezes and becomes ice. It can be air when it evaporates and forms water vapors.