Tons of stretch.  If you're going for a more "dressy" fitted look then size down.  Ash is a 16 pictured in the 16 but can do the large also if she was dressing them up to go out of the house.

Sizing

S 2-6 

M 8-10

L 12-14

XL 16-18

1x 18-20

2x 20-22

3x 22-24

Measurements (taken while laying flat)

Inseam from crotch to inside bottom seam

S-XL: 29 Inches

1X-3X: 29 Inches 

Rise from crotch to top front button

S-XL: 10 Inches

1X-3X: 12.5 Inches