Anyone have issues with how they calculate calories burned?

misslissa121

My kids' school is located on a circle so after doing what needed to be done with dropping them off and PTA stuff me and another volunteer go and do a few rounds around the circle (approx. 1 mile each) Today was 2 laps at 40 minutes so I put in my exercise walking at 3mph for 40 minutes. I came home with my two youngest half day kids and then we walked to the school to get my son. It is a pretty hilly walk, but would probably calculate out to flat land, but I was also pulling 50+lbs, my three year old twins) Why is pulling a stroller for 35 minutes (total time walking to and from the school) less calories burned (142) than when you straight up walk.