We'll hang out and have fun. We won't be bossy, and no one has to smile if they don't feel like it. We'll let the children take some pictures on our big cameras so they're not intimidated. Don't worry about making it perfect: when all the babies are grown and having babies of their own, the real-life shots will mean more than the posed ones. Your shoot will be really easy – well, as easy as normal life with normal kiddos can be. And the end result will be true-to-life, natural family portraits with no dodgy matching outfits or weird cheesy posing (unless you're big Awkward Family Photo fans and want dodgy matching outfits and weird cheesy posing).
One of the major thing we've learned on our London baby photographer adventures is that adults tend to think that children are the difficult ones to photograph. It's not true at all. They consequently spend the entire shoot distracted by that, thereby ensuring that they become the "difficult" ones themselves.