Even if all the world were to combine forces, they could not bring about the conception of a single child in any woman's womb nor cause it to be born; that is wholly the work of God.
It's not only children who grow. Parents do too...
Certainly, people can get along without siblings. Single children do, and there are people who have irreparably estranged relationships with their siblings who live full and satisfying lives, but to have siblings and not make the most of that resource is squandering one of the greatest interpersonal resources you'll ever have.
I belong to a tradition that believes that the death of a single child is a blemish on creation...