Consider this as well: if you're a primitive human and you have to take your baby somewhere, you're going to be praying to whatever deity(s) you believe are watching over you that your baby understands the severity of the situation and doesn't start screaming in the middle of the jungle. 'cause if it does, every predator in a 5 mile radius is going to hear your baby screaming and dinner bells will start going off in their heads. Our only major survival traits are our near-infinite stamina (if properly trained) and ability to magically fuse or deform useless objects into something useful. Additionally, the usefulness of both of those traits diminishes with the size of the group as a single human with a spear is far less likely to survive a tiger attack than two humans with spears. To put it another way, your baby will actively alert predators that you're burdened with its existence and that you could be free food so that you get removed from the gene pool if you're stupid or unlucky enough to travel alone.