It's a little late to be unable to speak at the age of four, but as long as you are sure that Bao's pronunciation is ok and you have called your mother, don't worry. If you have something to say, you can ask Baoduo. When you talk to him, repeat the key points several times. Usually you can watch cartoons with him and play early education videos with your children outside. It is easier to learn to speak with children of the same age.

The key is whether he won't say or not!