We recommend choosing the smaller size if you are struggling to choose between two of them. Our sleeping bags run big. This size guide based on height might be helpful:

Size 1 year: between 70 cm and 80 cm.
Size 2 years: between 80 cm and 90 cm.
Size 3 years: between 90 cm and 100 cm.
Size 4 years: between 100 cm and 110 cm.