Yes I do. Neighbour my age growing up was an only child and adopted - we used to play with him all the time but he was left out abit at school too.(sad)
In a big family - parents have to keep an eye on all the kids and too busy & lose track so kids can get up to stuff without parents knowing. Thats fun.
When an only child all eyes are on you, I'd say + you'd have to account more for every move, its harder to get away with anything crazy (like running away from home)- no other sibling to blame and you then have to entertain yourself most of the time. Its alot. I definately think its more responsibility on them and expectation too. I know they can get spoilt, there is that but thats OK.
I'm the youngest of 4. I used to hang around slaughter houses, and try to open coffins in the church as a child, that sort of thing... had parish priest visit to have a word with me a few times when I was 8.
Sisters 11 yrs and 17 yrs older than me and brother a year. We have no contact at all.
Interaction with other kids has more advantages I'd say but only children do cope very well - as I think they are so used to relying on themselves - hopefully have more fun as adults.