If so, flush when he's not there. Other children like to flush the toilet themselves. Some children are trained in just a few days. They decide that they want to be like older children and adults. Other children are trained very gradually over a period of weeks.
Most children have accidents after they're trained.
You should act casual about this. But while your attitude is consistent, it can also be casual. It does not matter. Whatever he wants to do is fine. After all, he should have a lot to say about it.