I think, you first need to check with the doctor whether this is a flat foot or not, and even if it is then also there is no need to worry as some degree of flat foot decreases with age. Say, by the time kid turns 7 or 8. And if the kid has no symptoms attached to flat feet, should be left alone. Also, for flat footed children, all one requires is, have simple footwear, a well-fitted, supportive shoe with built-in arch support is generally the best. I suggest, talk to the doctor or podiatrist and let him assess the child's feet and advice as what should be the course of action. To know more on the condition, I came across a few links that you may want to read. Hope they help. http://www.abc.net.au/health/talkinghealth/factbuster/stories/2009/08/13/2654510.htm https://www.betterhealth.vic.gov.au/health/healthyliving/feet-children
As kids grow, some of these conditions correct themselves without treatment. Others don't or become more severe because of other medical conditions. But many orthopedic (bone) conditions, just like dimples or cleft chins, are just normal variations that don't need to be treated. If you still feel worried about it, raise it up with your PD during the next routine check and see what he says. I have not much knowledge about it. It would be helpful to hear more from you :) sharing amd exchanging information is good knowledge.