My advice, it might sound anecdotal but just give it a shot, make sure your boy sings all the songs he likes 24/7, make him learn new songs and give him a recorder to record and play songs, there's research by the university of helsinki that singing repairs the brains speech centers and remodels it, it's worth giving it a shot, i personally have incorporated singing 24/7 and i'm very fluent now, couldn't speak even letters normally.