The pattern includes instruction for 4 sizes:

3-6 months (275 meters yarn)
chest circumference - 18.75 inches (48 cm)
Length - 10 inches (25.5 cm)

6-12 months (350 meters yarn)
chest circumference - 21.5 inches (54 cm)
Length - 11.25 inches (28.5 cm)

12-24 months (450 meters yarn)
chest circumference - 22.75 inches (58 cm)
Length - 12.75 inches (32.5 cm)

2-3/4 months (520 meters yarn)
chest circumference - 26.75 inches (68 cm)
Length - 13.5 inches (34.5 cm)

Video tutorial for 12-24 months is available in my YouTube channel
https://youtu.be/X2xZ5p_17oc?si=qYFTy0O8lKwDLbpC