I think your child needs a diagnostic laparoscopy to make certain there is no testicle in the abdomen. There is no other test that can confirm this other than blood tests (serum testosterone levels will be low and LH, FSH levels will be high). At the time of this procedure he can have artificial testes implanted on both sides for cosmesis. Testicular transplant is not an option that is available. As I said before, he is likely to require hormonal supplementation for which you should consult a paediatric endocrinologist.