See the size guide here

A brand already recognized for designing respectful footwear that provides free movement for babies and young children, and does not interfere with the correct development of the feet. Young children sense their environment and move their feet and fingers freely.
It's as if they were walking barefoot!

Composition: Textile. - Cotton.
Sole: TPR Rubber - Lightweight and highly resistant to slipping. And the wide toecap, to give space for little fingers to be comfortable, allowing better motor development.

Sustainability: Concern about the materials used. The fabric is made from sustainable cotton and the rubber is non-toxic.
Care: Hand washing recommended. Machine wash, only on a program for delicate items, placing in a special perforated mesh bag.
Other information: Designed by the Center for Cognitive and Behavioral Development at the University of Seoul. Recommended for use from the crawling stage until around 3 years old.

Reference: ATTABO03