A child isn't mature enough to think objectively about such a weighty subject. Their level of reasoning is too immature; not until adolescence does a person have a reasonably well developed ability to understand "gray" abstract concepts, and issues that don't directly relate to themselves. To a child, everything is black and white, and everything is about themselves.

A child exposed to such propaganda would be more apt to think they are a bad person for eating chicken, rather than KFC the corporation is wrong for treating chickens badly.

This is, of course, exactly what PETA wants.