The speechless child

Of all the things that didn't make sense to me in this movie, the child not talking was the worst. I mean: if that child NEVER spoke since it was born, and he is almost 11 years old, that should worry the parents. The child would be in therapy, right? No sign of this whatsoever.
But if the child stopped speaking after the move to the new house, that should be doubly worrying. Obviously he did not want to move. But nobody, absolutely NOBODY in this film seemed to think it strange that a child of his age doesn't utter a word - ever.

Plothole after plothole, but to me this was the most annoying.