An easier activity to organise and control might be a giant Bingo. But, you have stated that your task is to make the children talk. Games, as I posted above, are ideal for speaking whereas Bingo is more of a listening activity. With a little bit of creative thinking, it might be possible to turn it into a listening and speaking activity.
Then, if you can sit the children down in rows or at desks, you can also play relay races or broken telephone. You could put the more experienced children as group leaders and this type of game would give you the opportunity to drill vocabulary as a huge group beforehand.
Again, these are just some ideas to think about. If any of them interest you then we can get into more detail on how to go about them and organise them.
I've put more detail in this article on
ESL Games and Activities for Large Classes.
I hope this helps.