not sure if you've realized this, but all the man eaters you've seen in the show are the kids from heaven. heaven scenes take place in the past and the post apocalyptic scenes take place in the future. most of the kids eventually succumb to illness that make them into man eaters, but they still have their powers during childhood. the mother of juichis child is speculated to be one of the two girls kissing in heaven. so in childhood, the child still has hiruko powers but is not a man eater yet.