Lengths from the top of the shoulder to the bottom of the hem (may vary slightly):  

Size	Length
6 mos	16”
12 mos	18”
18 mos	19”
24 mos	20 ½”
2 T	22 ½’
3 T	25”
4 T	27”
5 yrs	29”
6/6x yrs	31 ½”
7 yrs	34”
8/10 yrs	36”