that YOU knew nothing about it since there were no statisticians with doctorate degrees, in addition, at these times. So: statistically unproven
there is no need to have lived at that time to make statistics on the stories that we have, at least during the historical period. So what is the answer for you?
on the one hand, history is made according to needs. Thus, are we going to find the relations of a battle between two countries, and not the same discourse according to whether the historians belonged to the victors or the vanquished.
To return to the mortality of children, (and why less than 10 years?) In times of famine, war or epidemic, (often the three together precisely) mortality is higher than in normal times and in cities , more than in the countryside and we talk much more about what is going wrong than what is going well, just listen to current information or tales of yesteryear! So NO, we do not know anything specific and credible about distant times to make real statistics.
"We make science with facts, like making a house with stones: but an accumulation of facts is no more a science than a pile of stones is a house" Henri Poincaré