Instead of using a sewing machine that is complicated to use, choose the simplest machine. As a beginner, you must have learned to sew on the sewing machine, which is simple and after getting a lot of experience, jumped on the advanced version. In the same way, look for the simple machine for your child and let him learn about the basic configuration of the sewing machine.
Without basic learning, it is not possible to learn about advanced techniques, as well as configuration. Let your child learn slowly and never rush things. Let them enjoy the work and increase their confidence when they are at the machine.