Your child will not complain if he wears shoes that are three sizes too small - This is not even noticed by children.
For one thing, children's feet are very soft and flexible. Foot bones and cartilage do not yet have the strength of adult feet. Secondly, the nerves in the feet are not yet fully developed. The signal "My shoe pinches" is therefore not transmitted to the brain. The wrong shoe size for children can have fatal consequences. Studies show that 69% of all children wear shoes that are too small and 88% wear slippers that are too small. This is alarming and has devastating consequences for foot development. Shoes that are too small and too tight change the position of the toes. The malpositioning of the feet has a long-term negative effect on joints, muscles and the musculoskeletal system. The result: more than 40% of all adults suffer from foot and posture problems. The development of children's feet is completed by puberty - often the damage is already done by then.
Always make sure you get the right size when buying shoes, finkli, boots, etc. How to find out the right shoe number for your child can be seen here in the simply explained video from Vögele Shoes: https://ch-de.voegele-shoes.com/kinderfuesse-messen