A child in a family is neither first or last is called the middle child. In a 3 child family, it is the 2nd child, etc.
This child usually gets the least amount of attention, because he/she is not the parent's first, and not deemed as 'special' enough, and is not the parent's last, and so is not treated like the baby.
This creates social tension between the family. The middle child would be the outcast while the rest of the family can have a laugh with each other.
However, in a family where there are seperate parents, creating half-siblings, where the child is in the middle of one side of the family, and is the first or only child in the other side, the middle child may become brattish, and demand everything he/she wants because he/she can get away with it with the other parent.
In the case of bratty middle children, the oldest usually looses out and then becomes the outcast, being independant and deals with how they recieve less attention than the middle child.
A usual night at the dinner table.
Older child doing A level maths: I got a B on a test today
Middle child still doing GCSEs: And? I got a B too.
Mum: *Surprised at middle child* well done (his/her name)! You're actually learning something then.
Older child: thinks; (>.> been there, done that. Pfft, middle child syndrome, lol)