Cracked skin most commonly occurs on the soles of the feet, especially the heels and big toes. Cracked skin in these areas is called juvenile plantar dermatosis. Deep cracks are painful and periodically bleed. The main cause is wearing wet shoes and socks or swimming a lot.
Cracks can also develop on the hands of children who frequently wash dishes or suck their thumbs.
Even deep cracks that have lasted for many years can heal in about 2 weeks if they are constantly covered with an ointment (like petroleum jelly). If the crack seems mildly infected, use an antibiotic ointment (a nonprescription item). Apply the ointment 4 times a day. Covering the ointment with a Band-Aid speeds recovery even more.
An even quicker solution is to cover long-lasting cracks with a crack sealer or bandage (a plastic coating that stays on and covers the crack for several days). A highly effective product is Nexcare skin crack care by 3M.