Yaaaaa, tough one as I'd really rather not physically force the toy out of my child's hand, but also believe that the toy should be given back. A few of my thoughts around this, as we spend a lot of time playing with other kids so inevitably it comes up lots:
- one mom thinks a lot about how she wants to treat her child as she herself would like to be treated, so when this child takes something from my daughter, we've all sat there while this mom spends 10-15 minutes trying to negotiate the thing back, and discuss it with her. I really admire the patience, and I can see how this would be wonderful in an ideal world, but what actually ends up happening is that my child ends up getting really upset during this time and I can't help but feel that the other child is getting the majority of the consideration in this scenario, and ultimately the mom has to physically remove the toy anyways, as this child has yet to give something back willingly. (also, in the adult world, we would be forced as well to give things back if we took them, by the police - extreme example, but it's a reality that kids need to learn IMO)
- all toys in the play area are for everyone to play with. If something is put away before the play date that's fair enough, but once all the kids are there, it doesn't matter whose toy it really is, if someone is playing with it they have a right to it. You can ask for it, and negotiate turns or whatever (with the help of the adults if need be), but you cannot take it away. If my child takes it away, I definitely explain that that is not okay, and use the "do you want to give it back yourself, or do you want me to give it back for you?"
- after quite a few months of hands on working through these scenarios, and being consistant on the expectations, it's rarely a problem now. Now it's just a meltdown because one wants what the other has, and we deal with that, rather than physically taking toys away.
- ALso, makes it a million times easier when everyone agrees on basic ground rules. ie it's hardly fair when my child has to share everything, and at someone elses house that child can take something away because it's their toy. However, life's not fair, and since I can't make everyone believe my way is the only way

we talk lots about how different families have different ways of living/different rules, and this is how we live!