Some children need more - attention, discipline, sometimes even material possessions. The parent who makes a valiant effort to even out the goodies at holidays or in quality time will always be in a bind. Can't be done. For the kids, there's more privilege in being older. More responsibility, too.
Some children get away with things by virtue of their place in the family or personal charm.
That life is unfair is certainly recognized by most of us. The playing field is not even, and it never was. Entitlements have always existed in the way of money and special access. Children of privilege have parents who hire tutors, pay for private schools and summer camps. Children of privilege have parents who know someone who knows someone who can get them summer jobs and internships and interviews.