Seems suspicious...
1) Some of the photos don't look that real. I don't want to be "that guy" who says he knows something is fake when he only has a hunch, but the last one in particular kind of looks like he was just Photoshopped in. Not saying they ARE fake. Just saying we don't know, which leads to my next point...
2) Even if they are real, the only thing that says the people are "underage" is the title on the Digg page. The TMZ page where the pictures are posted says nothing about them being underage. In fact, there's no word at all on who the people are, where the pictures came from, or when they were taken. For all we know, it could be him hanging out with some of his aides on a Friday night. I'll admit that seems a little out of character for John Kerry, but not as out of character as hanging out with a bunch of "underage drinkers."