This is exactly what I used to teach kids in the classroom I worked in. I was a teacher for a group of 3-5-year-olds. We would have "home toys" and "school toys." Some kids liked to have their home toys [only soft toys allowed] with them during certain activities.

Kids did amazing knowing that their "home toy" would be safe and that they would have to take turns with "school toys" because it belonged to Mr. Sam [the owner.]

"Mr. Sam is sharing his toys with you and we need to be nice with them, just like you want Susy to be nice to your Tiger toy."

"Mr. Sam doesn't mind if you share toys, but sometimes Jenny doesn't want to share her Tiger and that is fine. Jenny, if the tiger is going to be out, then we need to keep it in our lap, or put it in our cubby." Worked great. And the kids really learned when to share and how to say no--AND HOW TO ACCEPT NO without tears.