... unnecessary law because it purports to prevent a "harm" which is not a harm at all.

If this kid turns out to be one of that minority of gamblers that can't handle it and turns to crime to support his addiction, who pays for the costs to society? Old Dad? I think not.

An extrapallation of your argument would say that it is OK for the kid to get drunk, as long as it is dad's booze he is drinking or that it is OK for him to get stoned, as long as it is dad's drugs he is taking. No Thanks.

Many people consider gambling a harmless recreation. For some it is. For many more, it is a sinkhole where, although not bankrupting, siphons off a considerable amount of money that could be put to better use. (Not unlike chip collecting ) I would much rather hear a story of a parent teaching his kid how to fill out a deposit receipt at his bank or hand in a contribution to his churches collection plate.