In Arizona, A.R.S. § 13-3109 deals with the sale or gift of firearm to minors.

Except as permitted by law, a person who sells or gives to a minor, without written consent of the minor’s parent or legal guardian, a firearm, ammunition or a toy pistol by which dangerous and explosive substances may be discharged is guilty of a class 6 felony.[i]

The law however does not require reporting sales of firearms.  Registration of firearms or firearms sales is also not required under law.[ii]

[i] A.R.S. § 13-3109 (A)

[ii] A.R.S. § 13-3109 (B)