A medical practitioner may, by writing signed in the presence of a designated officer, certify that at the time of the certification—
(a) the medical practitioner had explained to a child referred to in section 12B the nature and effect of the removal from the body of the child of tissue specified in the consent and the nature of the transplantation; and
(b) the child understood the nature and effect of the removal of the tissue and the nature of the transplantation; and
(c) the child was in agreement with the consent given under section 12B .