Just looking for a little help. I want to grow my kids piggy bank. What is the best investment I can make for him?

My boy is 8 years old and has $500 in his piggy bank. We want to put that into something that will grow his money. I would
Love advice on the easiest way to start building up his piggy bank. We don’t do a good job of earning on our savings for ourselves but looking for some education to start a change in our lives so we can maximize our potential.