I recommend stories and songs in particular and of course games that CAN be played with larger groups.
There are plenty of games that can be played by thirty children without anyone having to wait for a turn.

For example a game I call Hot Potato, and I'm pretty sure it is also out there on the web by that name or another name. Here all the kids sit in a circle and pass round objects or flashcards, naming the card as they pass it. When you clap or say Stop!! the kids holding the flashcards come into the center of the circle and do a silly dance, or mime an animal or name some picture cards for you.

The above description is the final version but to start out with you need to introduce the game and you do this gently by first demonstrating with one picture only. As the children pass it round make it clear they must say the word in order to pass it. One cannot pass a picture without naming the item on the picture. At first just pass one card all the way round the circle. Now start again and this time after five children have passed the card feed in a second flashcard - of the same item to start out with, and keep feeding in more pictures until you have several going round at once.

Then once the children have the hang of that say stop!! and introduce the idea of those holding the cards coming in to the center.

Then when you play again feed in different flashcards.

Basically build it up element by element - you might be able to go quicker if you have a Chinese translator with you or if you speak Chinese yourself - it's much quicker just to explain the rules in L1 rather than do it all by demo.

There are plenty more such games on my site as well as twenty lovely stories (pic included of one of the characters) for that age group with matching songs. All in all everything you need! (But you need the primary games not the preschool ones as the primary ones are more for your size of class).

Shelley