Choosing bathrobe size not complicated issue and thanks to beach bisht creators they provide an easy way to choose bathrobe size.

Beach Bisht Kids Hooded Bathrobes comes with Small and Large sizes.

Size Suggestion
S: Recommended for sizes between 0.60 - 1.10 cm.
L: Recommended for sizes between 1.10 - 1.60 cm 

Beach Bisht Classic Bathrobes comes with Small Medium Large sizes

Beach Bisht Hoodie Bathrobes comes with Small Medium Large sizes

Size Suggestion
S: Recommended according to size between 1.50 - 1.65 cm
M: Recommended according to size between 1.65 - 1.85 cm
L: Recommended according to size between 1.85 - 2.10 cm