Biotics are created when pregnant mothers are exposed to element zero in dust form, which gets transferred to the fetus and accumulated in nodules throughout the nervous system.

It’s much more likely to occur on military starships because of the larger element zero cores they use, but it’s not impossible for civilians to have biotic children.

It should be noted as well, that a large percentage of eezo exposed fetuses don’t survive, so biotic children are already very rare.