Ooooh, I'm the middle of three girls. I don't think I was particularly traumatised by it, but there are certain memories (still) of what, at the time, seemed great injustices.
I was much closer in age to my elder sister than my younger, so the elder and I were often treated as a unit, and the younger on her own. To my own child's mind, this always seemed to play out in negative ways: 'you two are old enough to do the washing up, but younger isn't' 'you two need to behave properly and set an example to younger'. Or, on the other hand 'you can't do/get x, because you're not old enough' which would always be something that younger would be far too young to be bothered about. Another thing was that any successes I had at school, for example, were treated as routine, rather than great achievement, as elder had already done roughly as well as I did.
But as I said, I wasn't particularly traumatised by it and I can see the disadvantages to other positions in the family (well, the oldest, certainly, can't really think of any for being the youngest, though I'm sure someone will put me right). Also, due to certain other factors, I'm by far the most independent sister of the three (although baby still has time to change that).
As others have said, just treat them as individuals, try not to treat them as 'the boys' or 'the older/younger ones' and remember that however they turn out will have at least as much to do with personality and outside factors as it does with position in the family.