There are two little boys like this at dd's childcare centre.
However the staff have explained it to me over time and it's basically that they cry at drop offs (just like most other kids) but they get very teary around 3pm when lots of kids start to get picked up, they get upset because they think it's their mum coming to pick them up.
One of the little boys is in my mother's group. He is a very loved happy child, except for these times. His mum agrees that the best way to deal with it is a quick cuddle and distraction, but after that, to just leave him be. She said if one of the staff try to sit with him until he stops, he just never does and wants to be held for hours (hes 2.5).
I know I trust my daycare staff, and whenever dd is upset they do comfort her, because they know that's what she needs and she will calm down quickly. I would just trust that the centre knows what works best for each individual child, because in the end it's not really my business to be asking them why they are/aren't comforting a child.
For example, this week a child was hysterical two days in a row when I went to pick dd up, and I was quite shocked and wondered why they let him be. I later found out his parents took away his dummy this week, and if the carers try to hold him he hits and bites them
so there's always two sides to each situation.