The heat source is a light bulb. Timing varies according to how much batter the child actually gets into the pan. Filling much over half full isn't recommended. Set a timer. Read a little story book or two.
Safety is the paramount issue.
The child needs oven mitts, supervision, etc., at all times. If the cake is not entirely done, but sets up enough to remove from the pan, the parent can try to ease it from the pan to a napkin and zap it very briefly in the microwave to finish the job. Test the oven before the baking session. It is dismal to get the batter in the pan and discover too late that the light bulb won't function. Interest in these toys waxes and wanes.