yes parents can get restraining orders for their children if the parents have custody and who ever they told to stay away from their minor children persists on seeing them.

in some places in the USA it is called -

stalking,
harassment,
grooming a child for possible future abuse,
encouraging delinquency in a minor
pedophilia

when an adult (someone 18yrs of age and above) continues to seek out contact with minors (anyone under the age of 18) after they have been told by the custodial parent no contact is allowed.

until the child is removed from the mothers and fathers care through the courts its up to the mother and father to make the decisions as to which adults (people 18 and above) their under aged son can be in contact with.

to the original poster-

the mother has told you no contact. if you really love this boy leave him alone, give him a chance to grow up, to be an adult. the mother says no more phone calls and no more visits behind the parents backs.

unless you want to be in trouble with the law for stalking, harassment and what ever else your location calls an 18 yr old chasing after a 16 yr old against the younger ones parents permission its time to back off and do what the mother said. time to leave him alone and let him grow up.

if the love you two have for each other is right and meant to be he will come find you in two yrs.