Severs disease is the popular name for a problem which should be called calcaneal apophysitis. It truly should not be referred to as Severs “disease” since it is not a disease. This is a self limiting disorder of the growth plate in the heel bone of kids that always goes away on its own eventually without having long term complications. This can be a extremely common disorder in kids about age 10 to 12 years and in the event you question a group of children of that age should they have it or have a friend who may have had it, then a lot of them will likely say yes. There is a growth plate behind the heel bone where growth of that bone happens at. The achilles tendon connects to this growth area, so its not difficult to see that lots of force is put on the growing area, especially if the child is overweight or busy in sports activity. Severs disease is a stress of that growing area. The actual growing area combines with the remainder of the heel bone by the early teenage years, so it is just not feasible for it to be a problem past that.
Whilst Severs disease is self-limiting and they'll outgrow this, it is painful and can cause problems so does have to be treated. The best method is to focus on education about the ailment and the way to control exercise loads to help keep it under control. It's quite common to use ice on it after sports activity to help relieve the pain. Cushioned gel heel pads are often useful and may make it more bearable so they can continue with exercise. If you can find biomechanical issues, then proper foot orthotics may be required to correct that. The main element of the treatment is just handling the loads. Kids of that age need to be active and be a part of sport, which means this might be a problem.