Parents keep a close eye on their growing children, watching for proper development and being alert for any sign of a problem because small problems can have big implications. Pediatric flatfoot is a childhood condition that, if left untreated, can result in permanent deformity in adulthood. Flatfoot deformity makes mobility and exercise painful, increasing the risk of reduced cardiovascular health and obesity.To diagnose a pediatric flatfoot, a foot and ankle surgeon examines the child’s foot in weightbearing and nonweightbearing positions, both in and out of shoes. The physician also notes how the child walks and evaluates the foot’s range of motion. In some cases, flat feet are associated with issues of the hip and knee, so the physician may examine those as well.
For further detailed analysis, the physician may order imaging tests, such as an x-ray, CT scan, MRI or bone scan. Family history will be evaluated as well since the presence of flatfoot disorder in the family increases the possibility of flatfoot in the child.

Pediatric flatfoot can be divided into two categories, flexible and rigid. Flexible flatfoot is characterized by a normal arch when nonweightbearing, or sitting, and disappearance of the arch when standing.  There may or may not be symptoms. In the case of rigid flatfoot, however, the arch is stiff and flat when both sitting and standing. In most cases, children with rigid flatfoot display symptoms associated with the condition. In either case, flexible or rigid flatfoot, there are a variety of underlying reasons requiring different treatments.

Babies often appear to have flat feet due to cramped positioning inside the womb, and the symptoms will abate with time. In other cases, the surgeon recommends stretching exercises or a soft brace for a short period. Children who do not exhibit symptoms typically do not require treatment but will be monitored and reevaluated periodically by the foot and ankle surgeon.
​
For children who do exhibit symptoms, the physician may recommend physical therapy, shoe modifications, anti-inflammatory medications, such as ibuprofen to reduce pain and inflammation, or an orthotic device. This device fits inside the shoe and supports the structure of the foot. In some cases, surgery is the best alternative.

​Source:  https://www.foothealthfacts.org/article/pediatric-flatfoot-cause-for-alarm