I think it was the little girl feeding Nick the zombie.
Yeah, I'm leaning that way myself. They showed a kid naming them last week, the drawing this week, even commented about the girl mourning her dad over the zombie and her unwillingness to kill a zombie on the fence.
Originally I thought it was a Governor plant, but that kind of plan is obscenely risky unless the person is trying to get killed. Also, not all kids are Carl and some may process what's going on so much differently. Maybe the girl thinks being nice to them means they'll be nice or some other crazy kid shit.