This site says that the legal age for online gambling in AZ is 18, and for "land" gambling is 21, but does not mention penalties for violations.
According to Arizona code section 13-3301 "Regulated gambling" requires that
Beginning on June 1, 2003, none of the players is under twenty-one years of age.
According to 13-3302 Regulated ...
The relevant law is not so specific. It prohibits child abuse and child neglect which are defined only as general standards and not as specific rules.
This doesn't appear to be child neglect, indeed, the opposite to the extent that there is such a thing.
So, would it be child abuse? This would be up to the finder of fact to determine, and might depend upon ...