At the start of the outbreak, desperate parents were convinced there'd be a cure some day for their zombie children. Some paid huge sums to cryogenic facilities which promised to keep them safe until the cure was found. Of course, brain scans have shown that - though we might find a vaccine to protect the uninfected - there'll never be a cure. The infected's brains are almost entirely eaten away. And when those cryo facilities lost power... there were a lot of zombie children running loose.
The artefact can be found in Season 1 Mission 17: Information Exchange