A good tip to teach children to understand math is to use objects to help them visualize mathemathics. For example, if a child is learning about 3D shapes parts such as vertices, edges, and faces, it makes it easier to see what it looks like.
Once the child grasps the concepts, you can have him/her explain things in their own way. Having the child teach helps him/her retain the information longer. There’s no need to buy expensive math models in order to help children learn math.