What does your child know about pure thoughts?
In my experience with the baby spirits and children I work with, they are telepathic. They value truth and honesty, and purity of thought. They know if what someone is saying is congruent or not. And many of them find talking to be inefficient and inexact. It's much easier an effective to transmit a clear message than it is to translate it into words, relay it at that level, and have it translated back into energy.
To some of them, this is ridiculous and makes no sense at all. I have had clients where their children would not, did not talk. And in our session, I was able to show the child why it would be a good idea to speak. And in the next day or so, they start talking. It's not that they can't, at least in the cases I have witnessed and assisted.
If you are congruent through and through, they will respond differently than if you are speaking from a place of less clarity or if there is unresolved emotion in your communication.
How can you support them to experience ease of being, to maintain their knowing, to feel seen and valued for who they are? How can you be honest and truthful in everything you share with them, in a way that is appropriate for their developmental stage?