My son had his first bone density scan at the age of 11 years at a children’s hospital.  There is a chart for ’normal’ bone density, which showed his was below that of an average child his age (it was not compared to an adult chart!).  He has had 3 more scans over the last 5 years, which still show low bone density but it is increasing with age and higher testosterone levels produced during puberty.  Although I do give a bone supplement now (including calcium) the doctors advised against it, believing it unnecessary as his diet is not lacking.  I however felt it would not do any harm and am anxious to do all I can to improve his bones!