I tell me children that they need to be responsible for bringing me anything they don't want the daycare to play with BEFORE any children arrive for the day. Then we put it somewhere safe.
If the children do not bring me anything or bring out the special toy during the day then they have to share and I will not be responsible for grabbing it away from the daycare children whenever my children remember to feel possessive. lol
This has worked pretty well.
There are some toys that the kids and my kids fight over and I have thought of buying multiples but then I ask myself if that is realistic. In life none of them will get what they want all the time and there aren't always multiples of things - it is better that they learn the lifeskill of sharing and negotiating for turns