I took ds1 and ds2 to the park yesterday and after playing they had an ice cream. Ds1 then wanted to climb a tree (not high !!) so they both ran off lollies in hand. Ds2 then came back and asked me to hold his lolly saying "I don't mind if you lick it mummy". Two minutes later ds1 asked me to hold his lolly while he got down saying "Don't eat any".
This incident really sums up their personalities to a large extent. Don't get me wrong, ds1 can be generous and is very loving. But on the whole i would say ds2 is by far the more giving.
I would put this down to the firstborn not having had to share (on a large scale) before the second child came along. In my case 3 years. Whereas the secondborn has always had to share as there was someone there before him.
Does this ring true with your family ??