During their first months of life the feet of any child is flat. It's a normal condition rather than a defect.
Up to 3/4 years all children have flat feet. Flat foot is characterised by the contact of the entire sole with the ground, the foot is not arched and footprint shows a contact to the ground not only by the outer but also by the inner part of the sole.
For children, differently than adults, flat foot is physiological, it's a normal condition and must NOT be corrected with arch support or anatomical insoles, if not specifically advised by the paediatrician.
The foot develops correctly and strengthens thanks to the natural movement. During normal walking activities, above all on irregular surfaces, the work of foot muscles and its natural stimulation will gradually "tense" and then form the foot arch.
It is then always advisable to let children walk barefoot on sand, on grass or at home because this contributes to the formation of the foot arch and then to the correct development of feet.