I agree that the three year old should be given rewards for good behavior. I find that rewards ( mostly in the form of praise from the caregiver, with others such as the chair example) are FAR more effective than time outs or other forms of punishment. For the little one - when you are in the process of taking away a toy from her and giving it to its "owner" offer lots of praise for "sharing". I know it's not REAL sharing but it will be a way of teaching her that sharing is good. This has worked for some of mine who are not natural "sharers".