How long does it take to learn Spanish well?

Hi, learning process takes some time. It encompasses not only speaking, but also reading, listening and writing. In this sense, the more your child practices, the more he will achieve his goals. Practice on a daily basis is vital, specially for languages. Listening to podcasts (in Spotify you can find some), reading initial-level books or webs for children in Spanish could help him. As regards speaking, my advice for him is to practice with a teacher or some friend. He needs to be "inside" the language. Hope my comments helps him. Best.