What to wear
I recommend dressing smart casual; something that you feel comfortable in but looks like you put a bit of effort with. Avoid flip flops, crocs, cargo trousers, track bottoms etc. Think timeless - either neutral tones or bright colours but simple - avoid logos or any distracting busy prints. Coordinating outfits is good, anything too matching might look silly. Layers and/or wearing a dress looks great in maternity photos. Style your hair to your preference but remember ladies I want to connect with your gaze so try to keep hair covering half your face.
How to prepare the kids
First and foremost, I want everyone to enjoy themselves. Make sure you agree to a session that doesn't fall right before naptime and that the kids aren't hungry. A favourite toy or comforter may do this and this.