family groups: any tips?

So, posed family group shots. Not really my best area. I can pose them pretty well, but.... I'm wondering if anyone has any tips and tricks for getting natural smiles, any smile at all out of sullen teenagers and cranky seniors, and luring the attention and smiles of really little ones. And just general cooperation. All suggestions will be appreciated. [I generally preferred to either work w/ 1-2 faces at a time, or in a more candid manner, but sometimes you gotta do the group posed family balonese, with muddy knees, if you knows what I means)...