Here are some further guidelines for you to decide which size would be best for your child:

The Sizing is as follows:
• 0 - 6 Months: Height(in.) Up to 26, Weight (lb.) Up to 18, Chest 19.5, Shoulder to Hem 15
• 6 - 12 Months: Height(in.) 26-30, Weight (lb.) 18-23, Chest 20, Shoulder to Hem 16
• 12 - 18 Months: Height(in.) 30-33, Weight (lb.) 23-28, Chest 20.5, Shoulder to Hem 17.5
• 2T: Height(in.) 33-36, Weight (lb.) 28-31, Chest 21, Shoulder to Hem 20
• 3T: Height(in.) 36-39, Weight (lb.) 31-34, Chest 22, Shoulder to Hem 21.5
• 4T: Height(in.) 39-42, Weight (lb.) 34-38, Chest 23, Shoulder to Hem 23