The small size of the penis may not be such a worry at this age. He is entering puberty and the organ size will now increase. The presence of hair is a sign that he is entering the hormonally active period of puberty. The size may also appear smaller than it is because of the obesity and the presence of fat in the pubic area. The penis would appear buried in the fat. Try and control his weight by restrictions in the diet and encouraging physical activity. If things do not look better, please consult a paediatric endocrinologist in your town.