The girls had their 18-month check on Monday (a little late, I know...my darned knee surgery got in the way!)
Thing 1: 26 1/2 lbs, 32 inches
Thing 2: 24 1/2 lbs, 31 1/2 inches
Going by the appearance of their thighs/legs and their overall pudge, one would think the weight difference is at least 5 lbs. Plus, Daddy and I, and Nana all notice the weight difference when we carry each one. Either Thing 1's weight is all on her legs, or Thing 2 just keeps her weight elsewhere...hmmm.