One of his greatest theories that is useful for children's learning is the Concrete-Pictorial-Abstract (Enactive-Iconic-Symbolic) approach.
It is impossible to use only words to explain simple mathematical concepts to a young child, since those concepts cannot be further explained using words. You will run out of words to explain! What definitely does not work is to start from use just words and they don't "get it", then scold them for being stupid.
They have to learn buy touching and playing with things, then from looking at pictures and then using abstract words or reasoning.