This reply is probably too late for you but it could benefit the many teachers viewing your post.
With that number of children I'd be inclined to do a song, like this:
1. Introduce some key words in the song. Play a game like "Jump the Line" (in my games book). In brief: two columns of words on the board to left and right of line, you call out one of the words and the kids jump to the left or right - if there is no room for jumping they can put their left arm or right arm out. The movement makes it interactive. At first you only show two words, practise with those then feed in more to a max of six to eight new words. (Six would be get a higher success rate).
2. Next show an action for each word - you say the word and the kids make the relevant action.
3. Play the song and whenever one of the keywords comes up the kids make the relevant action.
4. Play a game like http://www.teachingenglishgames.com/games/relayrace.htm
In this game the children have a chance to say the new words for themselves now that they have heard them many times over in the above three activities.
Hope that goes well!.
Let me know!