We never worried, figured what went around came around, and as long as none of the kids were sick or snotty...
We even gave up worrying about the drink swapping, they all had water anyway and we noticed they drank more this way.
You could always just keep hold of the toy your dd has nabbed, tell the mum "sorry about this, I'll clean it" and give it a cursory wipe with a nappy wipe when your mg meet is finished. You'll probably be told not to worry anyway, they all do it.
Lara