I ask them to take it down, start a dialogue about underage drinking and all the concerns I have for their safety.
I ask them to untag themselves from the photo, but keep it on Facebook.
I can't do anything! If I tell them I don't approve, they may "Un-Friend" me and then I won't be able to see any of their activity, good or bad.
I tell their parents; this is their child.
Oh please - we all had a drink or two while underage. Teens will be teens.
My nieces and nephews would never Friend me on Facebook for this very reason.