I was one of 4 and as much as my parents favoured my brother it didnt do us girls any harm as you say you give the others a bit more attention to make up for it.
My sisters were a pair of cows always ganging up on me and getting me in trouble but then if i could get one of them on side then i was just as bad.
Its sibling rivalry they work it out amongst themselves, we are all best friends now with our children as close as we were, youll never see four cousins as close as my kids and thats because of all the fighting we had when we were little. Honestly an old family friend used to me that my sisters and i would be best friends when we grew up and i never believed him. Jen and kate will be best friends aswell and they will laugh at the things they used to do to get eachother in trouble.
If you want to avoid making a favourite with your own children then you just have to remember to give them all an equal say!!!!( good luck if you got 4
I hope this helps