Kids' Manners: Sharing
"Everybody shares" is the motto in my house. When one child has a treat, the other child automatically gets some. I also repeat this phrase when my children are fighting over a toy. Then I find out who had the toy first. I never assume that the youngest child gets the toy because the older child should just deal with it. This is not playing fair.
You can encourage the first child to hand over the toy in 10 minutes by using a timer. You can also get the children to figure out how they can both play with the toy: one child holds it while another child instructs what to do with it, like the "Simon Says" game. Then they switch roles.
A third way to encourage sharing is to ask each child to choose his favorite toy and have a sibling "keep it safe" for a couple of days. This process builds trust and appreciation for each other while reducing material possessiveness. The children may refuse this idea at first. It helps to explain that each of them will get to keep a toy safe for the other.
If the children still can't work out how to share, sometimes the toy has to be confiscated for a period of time. But this method is less effective than the others for encouraging sharing. Most children have so many other toys that a few missing ones aren't a big consequence.