I have all toddlers here who are not all on the same page with sharing quite yet.
When one arrives with a doll, blanket etc, it MUST stay in their cubby until nap. I make a point of saying to the child in front of their parent "Okay xxx lets put your xxx in your cubby until naptime" and if they cry they cry. Then at naptime we go out to my mudroom all together and each one gets their toy for nap. After nap we walk back out to the mudroom and put it back in their cubby until home time.