In episode 3 of the BBC’s Meet the Romans with Mary Beard, she says that only about 50% of children survived to the age of 10. There’s some discussion about the idea that all but the children of the wealthy would be engaged in manual labor by the time they were 5 or 6. Is that what killed them? Exhaustion? Work-related accidents? Malnutrition? Or did the manual labor make them more susceptible to disease?
The majority of the children that would die would die from birth or a disease in childhood. Birth in ancient times was a dangerous task without the help of modern medicine, especially when taking account the numerous complications that can arise. Disease will preliminary affect the young and the old. Take Ancient Rome for example, nutrition and sanitation would weaken the children to the point of death at the hand of a small illness like the flu.(1) Things like diarrhea could hit children hard. It is near to impossible to discern the death of a child in their skeleton. There is some work done in the epitaphs of children recently. There are some aspects of infanticide but not as many as is thought. Medea kills her children of course which is one of the most famous cases of a mother killing her children.(2) There was a discovery in Greece in agora in Athens that I had the pleasure of hearing a lecture on.. There is a well that was a discovery with hundreds of juvenile bones. The original thought was infanticide, but many of the children were stillborn or had a number of birth defects. (3) I hope this answers some of your questions on child mortality. 1 2 3 I recommend reading one of my favorites books on disease if you are interested in disease in the ancient world "Disease and Medicine in World History" by Sheldon Watts