Manga about possessed child who develops a taste for people
We confirmed in chat that this is Kurozakuro. Here's the plot synopsis from MyAnimeList:


  This is the story of a wuss named Sakurai Mikito who one day swallows the creation of a creature called Zakuro and becomes an "oni", a superhuman creature with a taste for human flesh. As Mikito is horrified by this change in his once-gentle nature, he decides to leave on a journey with an oni-hunter in order to discover a way to turn back to normal.


Essentially everything matches the description in the OP. The first volume of the manga was released in English in November 2010 by Viz media. The series was finished in English at 7 volumes a year later in November 2011.

Here's the (Japanese) volume 1 cover: