my dc 18mths goes to quite a lot of playgroups. Often other kids snatch his toys and I tend to just distract him give / give him something else to play with. other mums don't tend to intervene.
But a couple of times he's taken things from other kids and I always immediatedly take them off him and give them back.
not sure if I am being too heavy handed with him as today when I took something off him (toy car) he got really upset. the boy who'd had it previously (about 2.5) didn't seem at all bothered when it was taken.
some mums just tell their kids to "play nicely" when they snatch. Perhaps I should just do that?