3 years not walk yet ?

Dear Mothers/parents, I have a son of 3 years old, he looks ok, he has done with MRI scan, all turns to okay. No reason that he can not walk, but still, he could not. He can hold things, walking a long. Without support, he can not walk. He can not stand on his own. Seems to me, he has no balance at all. He can bike and bike well. Any mother, father has any experience, pls help to give some advise as I am now very worry, no word to say..very frustrated. Thank you all for your reading . An