I have 2 girls, 7 & 5. The 7yr old is tall & thin, like a ballerina or dancer, needs size 6-8 on shirts depending on style, 7/8 on dresses due to torso length, & size 6 on pants mainly for length of her legs. However, with shorts or capris, where length is not so critical, she can still fit size 4T waist, & some 3T shorts.
The 5yr old is shorter, & stockier (think 5yr old linebacker). Not overweight, just bigger frame. She is pretty steady right now with size 5/6 on just about everything. Pants are sometimes a little long, but needed for waist size. Size 6 for dresses. Currently wearing size 11/12 toddler size shoes. 7yr old is in girls size 2. Weight wise, they are pretty close. During this next year, we feel the girls will end up in the same sizes. Then who knows what will happen by next summer.