I wonder how much those boxes weigh. I looked into the conversion tables and found out that "peck" is a measure of volume equal to two gallons. I suppose two gallons of milk on each arm would give a reasonable approximation of what this girl is carrying. Although the picture is focused on the girl, the cranberry pickers in the background look to me to be anywhere from a hundred to three hundred yards away.
A long way to walk carrying four gallons.

This little girl probably lived at 1216 Annin St which would put her in the middle of where most of the Italian immigrants lived at that time. I remember hearing the old timers saying that when they were kids they missed the start of school because of summer farm work.