Originally Posted by
joedris 
If he's your best friend, then it certainly wouldn't hurt to sit down and have a talk with him. But don't expect any miracles. Pointing out the effect that their drinking is having on the children would probably be the best avenue of approach.
I agree with this. So many active alcoholics (myself included at the time) are under the delusion that their drinking is not hurting anyone. In a way, not commenting is feeding that delusion.
You may just plant that seed, that it is in fact hurting their kids. It may not be something they want to hear (I expect they will deny it & rationalize their drinking) but it is what they need to hear.