It’s strongly implied in the negative sense. If we want to play the definition game, here’s Merriam Webster’s definition:

exploit (verb)
1: to make productive use of : utilize
exploiting your talents
exploit your opponent’s weakness
2: to make use of meanly or unfairly for one’s own advantage
exploiting migrant farm workers

Definition 2 is what I’m referring to. A baby consuming is certainly using milk for its own advantage, but the mother also benefits from the exchange. The mother cares about the health and comfort of the baby, and providing her milk can certainly be something she wants to do. Your argument only makes sense if you think children “unfairly” use the parents’ labor for their own gain as well (they consume far more than they contribute to family finances), vs parents willingly giving food and gifts to their children because they want to see them be happy and healthy.

The point here is “meanly or unfairly,” and a mother willingly giving her milk to her baby goes exactly counter to that.

Now, if the baby snuck into the mother’s bed and suckled without any consent or if the husband refused to purchase alternatives and essentially forced the mother to provide milk, I could see your point. But if the mother is choosing to give it, I honestly don’t see how that has anything to do with exploitation, at least in the negative sense. In the positive sense, humans absolutely exploit animals (e.g. vegans eat fruit and veggies pollinated by bees; humans are “exploiting” the bees, but the bees are also “exploiting” the flowers for pollen and nectar).