Kids usually listen and speak English at school. This is their social skill, self develop. No special need to talk with them in English at home generally. To keep good relationship and harmonized environment at home, talk with your own language is enough.
Btw 我覺得家長要有一定的英文程度。部份通告只有英文。大部份功課都是英文,不識睇instruction,就做唔到功課。連visual art 都是英文,除非日日補習啦。我為左個仔快些catch up oral english,我在家刻意講英文,以前是廣東話的,他不喜歡我說英文,在自己房門贴上字條“do not speak english”.笑了!