When a child with flexible flatfoot stands, the arch of the foot disappears. Upon sitting or when the child is on tiptoes, the arch reappears. Although called “flexible flatfoot,” this condition always affects both feet.

A tarsal coalition is an abnormal connection of two or more bones in the foot. The bones affected — called tarsal bones — are located toward the back of the foot and in the heel, and the connection of the bones can result in a severe, rigid flatfoot.

The accessory navicular (os navicularum or os tibiale externum) is an extra bone or piece of cartilage located on the inner side of the foot just above the arch. It is incorporated within the posterior tibial tendon, which attaches in this area.

Toe walking is a pattern of walking in which a child walks on balls of his or her feet, with no contact between the heels and ground. Toe walking is common in children who are learning to walk.

Calcaneal apophysitis is a painful inflammation of the heel’s growth plate. It typically affects children between the ages of 8 and 14 years old, because the calcaneus is not fully developed.