Infantry, as the name implies, is a collection of infants armed with weaponry that are used in military events such as skirmishes and battles, generally across Europe. Training is minimal and armies rely on the infants to use their gut instinct in battle, i.e. cry to distract the enemy, then hopefully point a gun at him, shoot, and kill him. It's a slim chance of actually happening, but they figured with enough armed babies, eventually one of them would get the job done in the battle field.
Of course, France got to the point where they couldn't arm them with guns anymore, so they started distributing sharpened sticks, and soon enough, became too lazy to sharpen all of them and just gave them sticks they found on the ground. Rocks were a rare commodity.
Eventually, it became too much of a hassle to feed the babies, so unwanted children were simply thrown out into the battle ground to be blown up by mortar fire. It was an efficient population control system, and was an easy fallback for women who couldn't stop getting pregnant. Some sick people really got off on this kind of stuff, and they make up the mass of 4chan today.