In essence
The best advice is to choose clothes that you feel comfortable in, and that are as simple and neutral as possible. Choose clothes without an illustration, text, or logo on. For adults, one plain color is best. Mums, choose clothes with a bit of texture for the most flattering effect.
For children, stripes or spots are okay, but they can be a bit distracting if the colors are bold. If you'd rather have something vibrant, go for it! You can also change outfits partway through the session if you'd like – when we head outdoors can be a great time to do this. Bear in mind your child's willingness to change clothes, though – if your baby really doesn't like being changed, it's better to minimize the number of outfit changes.
Take your watches off beforehand, to give the skin a chance to relax and any watch marks to disappear. Watches can be quite distracting in close-ups of you.. The same goes for hairbands on wrists. I'm very happy to offer advice based on my experience – if you have a selection of clothes ready, I can recommend which will work best.