I think your brother's son may be suffering from multiple nutritional deficiencies. Do you mean to say his haemoglobin
is 7? Then is definitely low. The condition is called Anaemia. The common cause is due to nutritional iron deficiency
. I also doubt that he may be having multiple other nutritional deficiencies as well.
Please take him to an expert paediatrician or a nutritionist, get his basic blood counts done and may be start on iron and multivitamin
Also, get his growth hormone assayed to look for growth hormone deficiency
Hope this helps.