Dear Baru,dont worry and panic.tell ur nephew to keep 2-3 pillows below his calf and ankle to keep the legs elevated.from the body level and lie in this position for few mins to hours.u can also apply a crepe bandage in afigure of 8(cross the straps over each other )nt too tight and nt too loose,bt firm.remove while he sleeps 4 along time.watch if it recides in 1 - 2days or else see a doc.i think it will work.am a physio so telling u by exp.gud luck.
You really should take him to see a doctor. This is very odd for a young boy to have. May need to have a referral for Lymphatic Drainage specialist. My doctor is in Central his ph no is 28497822.