The kids try to stay close to Helen when she's in the dome, otherwise they wander about the non-quarantined areas. They're not allowed outside unless Helen or Eddie is leaving and taking them with her or him, so they should be easy to find. Not all of the children have ailments that can be cured:
Ribera has an old broken arm that set poorly but can be re-set. He also has an old bullet lodged in a healed wound - not near any vital organs, but it could be taken out.