Any parent speak language other than english as main language to Lo.. How you manage to make Lo understand english while in school? t.i.a

My young man speaks English and Mandarin to my hubby and myself. He speaks Cantonese to his grandparents. He has been told from young that language is a powerful tool to make him outstanding in the crowd in the future. The key point here is don't mix the languages and practise to speak in good sentences and a proper way.