They breastfed until the children were three or four. Poor women. They were taking their calories and nutrients for all that time. They must have been toothless by the end, not to mention their breasts must have been mangled.

"The team sampled minute amounts from nearly 40 fossilised teeth of our South African fossil relatives, early Homo, Paranthropus robustus and Australopithecus africanus.They measured the proportions of their stable calcium isotopes in the tooth enamel, which are a function of the mother milk intake by infants.
By reconstructing the age at tooth enamel development, they show that early Homo offspring was breastfed in significant proportions until the age of around three to four years, which likely played a role in the apparition of traits that are specific to human lineage, such as the brain development.
In contrast, infants of Paranthropus robustus, that became extinct around one million years ago and were a more robust species in terms of dental anatomy, as well as infants of Australopithecus africanus, stopped drinking sizeable proportions of mother milk in the course of the first months of life.
These differences in nursing behaviours likely come with major changes in the social structures of groups as well as the time between the birth of one child and the birth of the next."