No one wants to be called FAT, even if they are pregnant

My students walked into my classroom today and one little boys says "Whoa you are fat today!"...awkward right...well then another little boy (trying to be polite) said to him "She's having a baby, she should be getting fatter everyday...". It just reminded me that yes, getting a bigger belly is a sign that hopefully baby is healthy and growing. However even a pregnant women does not take being called "FAT" in any sort a compliment.