Hi.. Horse shoe kidney occurs due to developmental fusion of both the kidneys at the poles... Well on most occasions they do not cause any major problems and your son can have a normal life like any other child.. Rarely they can cause problems like kidney stone, obstruction to the ureter leading to hydroneprosis, infection, cancer and so on.. And in some they may be associated with other congenital abnormalities such as down syndrome.. If no such congenital deformities are present, there are high chances that he may be asymptomatic and without serious problems.. My wishes and prayers are with him..