What to wear

Avoid bright yellows, reds and oranges as they draw attention away from the face of the subject and can cause a colour cast on the skin.
Avoid clothing containing logos, slogans, or other distractions.
Bold stripes, large designs and polka dots stand out and tend to draw attention from the portrait's subject.
Avoid short sleeved tops or shorts. When arms and legs are exposed and there’s lots of skin visible, it can be a distraction from the main focal point of the photo - the face.

White long sleeved tops and blue jeans always work well particularly on a white background.
Black tops can also work well with a white background but this is a high contrast and leads to photographs with a very different style.
Also consider wearing a top that has an interesting collar and/or sleeves.
A top that has interesting textures (e.g. a sweater) can also add depth and richness to an image. If you will have more than one change of clothing for your session then consider bringing a variety of necklines, textures, colors, and undergarments to achieve a wide variety of looks.
Stick to solids and subtle patterns.

Simple and elegant is the advice when selecting jewellery for a portrait. The same applies for any other accessories that you wish to have included in your portrait.

A comb or brush and hair-spray if you use it
A light face powder to reduce any shine on your face that may build up during your shoot.
For gents (or women who prefer not to wear much or any makeup), bring a lip balm. Dry lips don't show well in photos and so a non-shiny, non-waxy, none coloured lip balm is essential. Avoid chap sticks, as they tend to leave a white residue.
If you normally wear makeup, bring it with you but avoid high gloss lipsticks or very shiny lip gloss. Often they look too unnatural and reflect too much light in photos.

There are lots of clothing options for a maternity portrait each can be used with different lighting and backdrop styles:
White blouse, with lacey cuffs with a few buttons fastened and your bump on show, this works really well with a white backdrop.
Cropped top and casual trousers/tracksuit bottoms in a dark colour; this can be effective with either a white or black backdrop. When using the black background moody lighting is used to add shadows and depth to your portrait.
Wearing some pretty lingerie. You can go for the bright and happy look, you looking beautiful and confident against a white background.
Nude, posed beautifully to show just what you want to show; relaxed, warm and comfortable.
Wrapped in a sheet, just below your bump. (White or black - to match the background).
Since your bump will be exposed, it is important that, for a couple of hours before the shoot, you don't wear any tightly fitting clothes across it (we don't want any marks left by waist bands etc), likewise for any other areas that are likely to be exposed.

Toddlers photograph best in simple clothing. White and pastels are classic choices.
Newborns and babies have gorgeous skin, and nothing shows off that natural, innocent soul like nakedness (or just a nappy). An added bonus for slightly older babies, is that eyes tend to stand out more when they are not overpowered by clothing.
Don't be afraid to put your baby or child in bold colours or prints. Although not generally recommend for an adult (or newborns), vivid colours on young children will result in a playful, lively portrait, especially primary colours like red, blue, and green.
If your child wears his Spiderman suit everyday, maybe you should let him wear it in a few pictures. Why not? You want pictures that capture that your little man really is, right? Besides, he may be much more willing to take other non-cape pictures afterwards. Props can be great addition, too, so consider bringing your child's favourite book, stuffed animal or toy.

Coordinate outfits. Everybody in the portrait should wear items that complement each other in style and colour. It is not necessary for all clothes to match, but they must make sense together. Choosing clothes with same or similar colours unifies the picture and keeps the focus on the people in the picture.