It is a question of love. The father or mother in your example chooses the life of his/her own child, because he or she loves it. However, even the parent in your example would not pretent that his child has more right to live than the other one. Right?

So this is not a question of justice or equal rights. It is a question of love. And I assume noone - except hardcore saints - would tell you that you can or should have the same feeling to everyone.

All you need is love