Doctors and nurses see them in precarious condition – when they are just born, usually early and with physical complications.
They are the babies of hospital intensive care nurseries, who often start their lives amid a tangle of tubing and in the ultra-protective confines of an incubator.
Most eventually go home to become thriving toddlers and, heavy sigh, teenagers – stages their caregivers during those fragile ICN days don't typically get to see.
On Saturday, Pennsylvania Hospital hosted an ICN reunion to give medical staff a chance to catch up with former infant patients and their families. Nearly 500 were expected to attend the gathering in the hospital's Elm Garden, where little fingers toiled over crafts and all ages gathered for a group photo.