I don't envy you; it's hard work. I think though that the golden rule here is to keep it as simple as possible. Meaning tons of repetition and never being afraid to go back over what you've been practicing again and again. Of course that also means that whilst you're keeping the language the same the exercises and presentation are varied. The other major thing I find when teaching young learners is the attention span - keeping activities under 5 minutes when they start getting bored.
A couple of useful links:
TPR (Total Physical Response) and
TEYL or Teaching English to Young Learners