DS1 is just 6 and DS2 is coming up 2. They generally get on well and play (fairly) nicely together, but DS1 is starting to get more possessive of his toys. He has a lot of books in his room that are just his (he's a real bookworm) and there are things like boardgames and Lego that DS2 is too small for that are DS1's sole preserve. But he's recently started saying that things like the toy cars, and the wooden puzzles that we recently dug out the cupboard for DS2, are his (DS1's)toys. Which they are - they were bought for him or given to him, before DS2 was around. But I had assumed that they would be shared toys.
I think that it's partly just sibling rivalry, and that we might also need to look at whether we're expecting too much of him and creating some jealousy. But I was wondering how other parents handled the issue of toys becoming shared?