Generally speaking, drum sets can last for years and years with very little maintenance work needed. All that really matters is the condition of the drum head, commonly known as the skin. It’s important that children understand from a young age that the sound of their drums largely depends on the drum head – its tension and whether or not it’s fully intact.
At the first sign of indentions or cracks in the surface of kids drum sets, you should swap out the skins. Sometimes tiny bumps will form in the drum heads, and they will change the pitch of the drums in a way that cannot be predicted. In order to increase the longevity of a drum head, reinforce with your child that the drums are meant to be hit right in the center, not outside along the frame.