M1A's count as military rifles, do they not? How about sporterized 03's?
15 yards, any centerfire revo...check
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Kids shoot (now being serious ) Probably needs to be a cutoff on ages, but in general maybe make sure they have something fun & easy to shoot as far as a rifle, and balloons or something else as a reactive target (full soda cans?) so they can see hits.
A .22 single shot is traditional, but maybe a .22 autoloader would be more fun? And an AR with adjustable stock would fit different kids? I'm sort of brainstorming here, certainly willing to loan a rifle for kids to shoot.