A useful tool I have found in our homeschooling is to teach children at a young age to draw using shapes instead of lines. On the left is a typical child’s drawing, something you would see from your average 4-6 year old. On the right is the same child’s first attempt at drawing using whole shapes instead of outlining with lines. Can you see the amazing improvement from the first to the second? It only takes about 5 minutes to demonstrate this to your child but it will dramatically increase their artistic ability in the coming years as they train their mind to see whole shapes and more acuaretly represent what is THERE as opposed to interpreting objects and then representing them abstractly with outlines. 
Happy drawing!