Onesies:
Newborn 5-8lbs, 17-21 inches
0-3mos 8-12lbs, 21-24 inches
3-6 mos 12-16lbs, 24-26 inches
6-9mos  16-20lbs, 26-28 inches
12mos   20-24lbs, 28-30inches
18mos  24-28lbs, 30-32 inches
24mos  28-32lbs, 32-34 inches

Tshirt:
2/3T
4/5T

Youth sizes also available from XS TO XL

*** size disclaimer***
We use Gerber Onesies. These tend to run on the smaller end of sizing so please go UP a size if you are unsure of the fit