The best way to boost fine-motor skills, study all kind of shapes and learn how to build objects is sculpting. It always starts with small and simple forms and often leads to more complex, realistic or fictional characters.
This activity is a strong opponent to flat screens and devices, that our children are vulnerable nowadays. It teaches multidimensional perspective, basics of design and geometry, and how to work with their hands. Kids usually obtain skills of the craft quickly and enjoy every new work, which turns to be better every time.