The poster includes an image of a dead chicken and the logos of poultry companies operating in New Zealand, with the words "100% cruel" on it.
It also says "these companies kill 120 million baby chickens within 6 weeks of age every year in NZ".
Hanlon says he is a hunter and his family mostly eats the meat he hunts, "from field to plate", something he takes pride in.
"Deer and pigs are pests to the farmers whose land I hunt on," he added.
The concerned dad says he believes the posts "could provoke a huge unnecessary and graphic thought in children's minds when they should be thinking about school".
Hanlon believes children do need to know where their food comes from but disagrees that these posters are the right way to go about educating them.
"Kids do need to know where their food comes from - but it's up to their parents to do it in their own time. My daughters helped me since a very young age processing animals I've harvested but I haven't put this on any other family ever," he said.
"I don't know who put [the posters] up. If the person feels this way my advice would be please keep in at their house and put these posters in their own living rooms/kids bedrooms - not at the lights where many many young kids cross that's f*****g cruel," he added.
Hanlon added that his family keeps chickens as pets and they wouldn't eat them.
"I'm more looking out for the other kids as mine are sweet with it but I bet any others would be horrified," he said.
Hanlon took to the local Facebook group to discuss the posters with the community, saying in a comment that his issue was with the fact the posters had been put up outside the primary school, rather than any other establishment.
He also believes it is no coincidence the poster was put up "just above the crossing buzzer, where the kids press it to cross after school".
"To the person who stuck these on the light posts outside Milford PRIMARY school - give ya self an uppercut," he wrote. "This isn't needed outside a primary where a few hundred kids are going to see it, seriously unfair!"
The post received mixed feedback from the community. While many agreed with the dad that it should be up to the teachers and the parents to educate children on these issues, others believed it is important for them to be exposed to these realities.
"Bit wrong eh, let the parents teach their kids - not a chickens corpse used as propaganda," one person commented.
"No point in traumatising them before they're old enough to come to terms with it. This is highly nuanced and relies heavily on personal opinion. How about we let kids be kids and quit trying to indoctrinate them for a change?" another Facebook user posted.
However, another person thinks children "need to know the horrors creatures go through to be eaten".
"I've seen those around, don't see a problem with them to be honest. Chickens are treated horrendously," someone else said.
Multiple people reported seeing the posters around the local area.