Arts and crafts are great but they are best for an art class rather than a language class in my humble opinion. Although four hours is a long enough session to include some colouring or making things but if one is teaching the more usual time slot then I think spending time making things is a bit of a time filler and there are more effective ways to spend the time, such as listening and speaking games where the children are using English.
Here are a couple of games to try out and they are adaptable for small and large classes, as in China the classes are often huge by European standards.
Free ESL game for children Fun ESL game for children