HI. As your son is only 6 lump on the bone is not likely to be due to cancer. I hope you have done at least X-ray of the affected part. X-ray may show this as an exostosis- a benign condition. As for the sores at the corners of the mouth- this is called angular stomatitis and the cause is vitamins and folic acid deficiency. The root cause may be bad eating habits/ enterocolitis of some sort. This deficiency also causes the reduced resistance of the body giving easy infections and loss of weight. I would suggest such a patient to be first clinically evaluated by a Pediatrician and / or Pediatric gastroenterologist- HE would suggest further tests on examination and would advise mutivitamins and folic acid in proper doses as also an antibiotic and metronidazole. I would advise you to give him Vit A one cap daily for 6 days and Calcirol sachet one every week for 3 weeks. ( if your Pediatrician does not write separately). This is going to help in a long run for a healthy baby. Give a shot of tablet for worms. Follow Orthopedic Surgeon for the growth at bone. I hope this helps you and your son to get a cure. Give a long term treatment and diet training is also a must ( I know how 6 year old are)