Usborne publish books aimed at children learning German. I have their picture book in which each page is themed and has small icons all round with the word (and the die/der/das bit). They also have a workbook and CD pack and flashcards but I've never used them so don't know how good they are.

However as FriendlyKiwi said it would be better to contact their school first as there may be a resource that they like to use.