faculty.webster.edu/corbetre/philosophy/children/aries.html

On Aries' view, childhood is a very new concept. It did not exist at all in the Medieval period, grew into existence in the upper classes in the 16th and 17th centuries, solidified itself somewhat more fully in the 18th century upper classes, and finally mushroomed on the scene of the 20th century in both the upper and lower classes. But, on his argument, childhood did not really penetrate the great masses of the lower and lower-middle classes until very late 19th and early 20th centuries.

Aries does not claim there were no young people. Not even a Frenchman would try a claim as bold as that. Rather, while there were an abundance of young humans between the ages of 7 and 15, they were not seen as children. Their cultures lacked the concept of childhood. In the Medieval world a young person of 7 was already an adult. (Recall that in Roman Catholic theology 7 is the age of reason, the age when one could begin to commit serious sin. This is an argument which Aries overlooked). Aries points out that most young people were apprenticed, became workers in the fields (later, after the industrial revolution, in the factories) and generally entered fully into the adult society at a very early age.