what is unusual about the children in the community?

All the children in the community have to be certified "normal" by the Elders. Thus the, children are all fall within a narrow set of "normal" perimeters. Children like Gabriel and Jonas are different. Jonas, in particular, has the gift of a kind of Extra Sensory Perception which leads him to the role of receiver of memories.

Oh yes, the children are not the product of parental unions, rather than they are spawned from separate women designated to birth children. These babies are then evaluated for "normalcy" and given to pre-accepted parental units.

The children have many "Unusual" features but that is only if you consider "Unusual" as things that the children of our world don't do. For example the children of our world can choose to wear whatever clothing they please, as for the children of their community they must all wear "Tunics". But that all depends on what you think of as " Unusual"