It is sort of the idea of redirection which parents are told to use rather than say no but I use the no and why and that until they play nicely they have to play alone then move them to another centre - it could be in front of the barn and animals or to the books or on the couch or table with puzzles. They have to play alone. And if another child goes to where they are then I say no child XXX needs some time to play alone. He wasn't playing like a nice friend. Then as the child tires of the area and starts looking around - what it does is help them gain their composure while giving their hands and mind something constructive to do - I tell them they may go and ask if they may play too - in other words can't just go and take over an activity.
We have that rule that some centres are group and some are alone if the child wants it to be alone but can also be shared if they want such as some of the fisherprice type sets.