Who gives a ****, the child of a billionaire is obviously going to have a somewhat different life and he's going to have access to alcohol whether or not Madonna wants it...it's a lot wiser to give him that herself so she can control how much and what he's consuming.
My parents were Ok with me drinking from 14/15 years old and I never had any issues with alcohol, now that I'm in my 20s I am able to perfectly control and moderate it and never feel bad or have too much because I learned how to deal with it from a young age.
There will probably be a lot of "omg she's such a bad mother" on this thread and perhaps in the media but it doesn't surprise me as most people are total prudes and have no idea how to handle their liquor