My top tip to what to wear to a photoshoot is to be comfortable. - if you're wearing something you like, you'll be more relaxed and happy and this will come across in the images.
I tend to suggest steering away from colours with loud patterns and logos - these can clash with the other people in the shoot and sometimes with your surroundings too. Muted, soft, natural colours look great - whites and greys are timeless and children look good in bright colours too.
Have a think about what you'll all be wearing and making sure you're not poles apart in terms of what you wear. I'm not suggesting that you all wear identical outfits, but similar colour palettes work very well.
Different colours also work well for different seasons. In summer white can sometimes look at bit harsh, but when the light is less strong, whites look fab! Likewise in autumn, autumnal colours can look great - mustard yellows are my all time favourites!
Here are some of my favourite images to provide some inspiration! Hopefully it will help.