If your godchild uses the referral link (accessible from the "Godchildren" / "Referral link" menu) that you have indicated to him, then he will automatically be attached to you, for life.
Otherwise, when registering, he/she can simply manually enter your sponsor code and/or your email address and it will be attached to you.
Your sponsor code is contained in your referral link, after the root "http://atrad.io/register/".
E.g.: your referral link is http://atrad.io/register/lastname247891, your referral code is lastname247891 .