wife and child visiting family in china

Hello My wife is Chinese and would like to visit her family in China in September, she is planning on taking our 18 month old son with her so her family can meet him, she lives in the UK on a marriage visa with myself but will apply for Indefinite leave to remain next month (may) Does our son need a full UK Passport and visa to travel to China with his mother, any information would be welcomed, many thanks in advance Mike.