Kindergarten

I have taught groups of 30 kids down to 5-6 kids (age: 4-5).

I find that it's easier to get the kids interacting with themselves for a longer period of time when there are more of them.
I don't think the games I used varied that much, only how we played them.
For example, "stations/run + slap" - With a small class, everyone can play. If you try it with a bigger class you either need a lot more space or the sts have to take it in turns. I usually have 4-5 groups (roughly 5 per great). This is good because they have to listen to a) which group and b) which item of vocab.

Hope that helps!

Thanks for that comment. My concern will be about maintaining their attention when they are not actively participating in a game. I like your idea of involving all of the groups at random, rather than focusing on just one at a time.
Ruth

Encourage the others groups to cheer the active group on. I think this makes it more enjoyable for everyone. It also helps to focus all the sts on the action (and really eager to be in the spotlight).