My son is 7 and has very flat feet.  I am concerned that this will cause him problems in the future.  Is there anything that we should be doing now for him?

If your son has a flexible flatfoot then there is typically nothing to worry about.  A kid with flexible flatfoot will have an arch in sitting that will disappear with weight bearing whereas a rigid flat foot will not present with an arch at all.  A rigid flatfoot is more likely to cause problems in the future, however not necessarily.  It is currently recommended that he stay strong with his foot muscles (go barefoot!).