TBH, I usually get down with DS and tell him to give the toy back and he can have it when the other child is finished. Or if the other child has had the toy ages, ask if the child wants to share. The child can give DS the toy. Happy children all around, and lesson learnt. Or they can just throw a tanty - they have to learn the world doesn't revolve around tantrums! Usually when I suggest sharing the children are open to it, it just doesn't come naturally.
That's exactly what I do