Well, there are two things you can do. First, learn a bit of their language - especially classroom language such as stand up, sit down, come here, go there, listen, let's sing, and so on. Second, if you're not sure what to teach or how and where to start, then begin with the children. Get to know them; find out what they can and can't do. Are the even interested in learning English? Motivation is a tough one in EFL. Why plan ahead when you don't know the situation. As for what to bring with you or to prepare for your lessons, you'll want to brings music (it's great for listening practice and for learning pronunciation), a grammar book (for your reference; good books help you with how to teach concepts that you may find diffuclt to explain), 2 or more activity books on how to teach English to children, a box of flashcards (nouns/things and verbs/actions) for the activities, children's books (for you to read to your students; choose one's with loads of pictures and easy English), a picture dictionary (You might need to use it too), an English dictionary, and that's as much as I can think of at this time.
Tell me, what's your teaching background? Do you have TEFL?