This section deals with giving a minor a handgun, which is not illegal but the child must have the parents written permission. It is not a straw-man purchase for a parent to purchase a long gun for their minor child but I can not locate the law at this moment. They must be able to lawfully purchase the gun theirselves if they were of age. No criminal record or restraining orders, mental problems, drug use. I can legally buy any person a gun and give it to them as a gift as long as that person can legally purchase a firearm theirself. Some states have laws though requiring that if you are purchasing the gun for a gift, such as your son, that before the transfer can be completed a background investigation has to be done on the person receiving the gift.
United States Code
TITLE 18 - CRIMES AND CRIMINAL PROCEDURE
PART I - CRIMES
CHAPTER 44 - FIREARMS
U.S. Code as of: 01/02/01
Section 922. Unlawful acts
"x)(1) It shall be unlawful for a person to sell, deliver, or
otherwise transfer to a person who the transferor knows or has
reasonable cause to believe is a juvenile -
(A) a handgun; or
(B) ammunition that is suitable for use only in a handgun.
(2) It shall be unlawful for any person who is a juvenile to
knowingly possess -
(A) a handgun; or
(B) ammunition that is suitable for use only in a handgun.
(3) This subsection does not apply to -
(A) a temporary transfer of a handgun or ammunition to a
juvenile or to the possession or use of a handgun or ammunition
by a juvenile if the handgun and ammunition are possessed and
used by the juvenile -
(i) in the course of employment, in the course of ranching or
farming related to activities at the residence of the juvenile
(or on property used for ranching or farming at which the
juvenile, with the permission of the property owner or lessee,
is performing activities related to the operation of the farm
or ranch),target practice, hunting, or a course of instruction
in the safe and lawful use of a handgun;
(ii) with the prior written consent of the juvenile's parent
or guardian who is not prohibited by Federal, State, or local
law from possessing a firearm, "