I've been surfing the Net in search for some new ideas and I found this one, I think I'll try it out tomorrow:
Toss The Smile (Icebreaker)
Children can sit in circle or throughout the room as long as everyone can see each other. Identify one child as the "smile tosser". All children are to keep a straight, serious face while the smile tosser smiles. The smile tosser will smile at all players trying to get them to crack a smile or laugh. If anyone smiles or laughs, they are out of the game. Those out of the game must be absolutely quiet during the rest of the game. The smile tosser can wipe off his smile with his hand and throw it to another player if he wishes. The receiving player will put on the smile and be the new smile tosser. You can even set a time limit on how long your smile tosser is allowed to keep his role.
Source: CLICK HERE
If you teach older kids, you might find this activity useful: CLICK HERE
It worked wonderfully with the quieter groups, but you have to be careful if your group is rather fidgety and gets carried away easily. In the latter case, it's better to leave it for the very last minutes of the lesson. In general, it is a very nice energiser-filler and helps the teacher to bond with the class.
It doesn't have to be an ice-breaker, though!