I'm always after my kids for a picture. They can tell you themselves how many times I've said, "You guys! Quit goofing around and be serious so I can have a nice picture of you together!"
For Christmas they had a friend take not one, but several "nice pictures together." And at the same time, they threw in a couple of silly ones for good measure, because of course...that's who they are.
I wouldn't have it any other way.