In my assessment, the eldest child has the advantage for a number of reasons.
The eldest child benefits from drawing the maximum amount of attention from the parents and the immediate family. The first child brings a unique sense of completeness to the family. A couple become parents, parents of the couple graduate to becoming grandparents, siblings of the couple graduate to aunts and uncles. This all rounded achievement for a family happens when the first child is born. It is for this reason that the first child carries a significant, special place in the heart of the family.
Αll the attention of the parents and the family go towards promoting the general well-being and development of this child. In the joy of their own graduation, they mostly go out of their way to offer the best quality care to this child. For the parents, while the eldest child brings a new joy, it also brings the unique curiosity of parenthood. In their quest of providing the best opportunities for development, they might invest in a wide range of classes and programmes to develop skills that they may think are relevant. For their subsequent children, the parents mostly try to repeat the best developmental experience amongst all their children; however, the eldest is spoilt for choices and opportunities and the subsequent children benefit from a preset parenting model that the parents had fine-tuned when parenting the eldest child. It can be argued that the first child is subject to experiment by the new parents and the subsequent children benefit more experienced parenting. However, in my opinion, exposure to variety even by way of experimental development activities can only be progressive to a child’s development.
Let me reiterate, I am not alluding to the fact that the subsequent children ( siblings of the eldest ) are not receiving love and attention, but for the reasons mentioned above, I strongly believe that the eldest child has a significant advantage.