First up, we have two small children of our own, so we know exactly what family life can be like. Don't worry. We'll just 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 things we've learned on our Los Angeles/London/Brighton family photography adventures is that adults tend to think that children are the difficult ones to photograph. It's not true at all. When the grown ups spend the entire shoot distracted by the idea that the kiddos are being difficult, that'd what can make a shoot start to feel less fun for everyone. So, a big part of being a family photographer is getting the grown ups to relax; the kiddos are easy. Now that we have children ourselves, we know relaxing is easier said than done. But, honestly, don't worry about it. If your toddler's temporarily gone demonic, it'll just make for more memorable pictures.