Favoritism does a lot of damage. I have two siblings, I'm very close with one, and don't talk to the other.
The middle child was a favorite, in fact I remember during the divorce my parents argued over who would get him. It wasn't because he was well behaved, it was because he struggled academically so he was wrapped in cotton wool.
I would say, don't turn your child into a baby sitter for their younger siblings. I was expected to cook, clean, and take care of my brothers. This caused huge resentment mostly because they didn't want to listen to their 'bossy' sister, who was just trying to remain in control of the situation. And I hated that they would leave messes every where and I'd get in trouble for it. I was never allowed to be the child, because there were two younger children. The main reason I don't get on with the middle brother is because I moved far away, and he saw me as the primary care giver (covered bills, cooked, cleaned etc) and hated that I was no longer there to support him, and felt abandoned. I stayed home until I was 22 to do that for them and didn't live my own life because I felt obliged to be a parent to them, because that is what my parents taught me to be. Ironically, the main reason me and the youngest are so close is because he see's me as more of a mother figure than our own mother haha
As a child we never shared, my parents would buy duplicates, usually in a different colour or something.