Unfortunately, I can't help in terms of toddler girls. But for my current 3yo son, he wears some bigger 2T sizes and some 3T. He's the average one in our family, his older brother and baby sister are small ones. I think it's also some brands are cut wider than others. Like I've notice Children's Place to be wider cut. Carter's fluctuates, Old Navy and Gap are average.
With all sizing, I do think it's a choice on how parents want to dress their kids...loose and baggy or fitting. I do the later, and so clothes look like the fit right now.