I published this blog originally a few years back, but its a question I regularly get asked by clients, even more so now that social distancing means parents are more involved in photos with their newborn as, for safety reasons, it is still not safe for a newborn photographer to get close enough to 'hands on' pose a baby as we did pre-Coronavirus.
While I'll always advise to wear whatever you are comfortable in, here are some general pointers.
Avoid bright colours such as reds, oranges and yellows as in the finished photo these colours will draw the viewer's eye away from the subject (i.e. your face!). Avoid bold stripes and loud patterns for the same reason. Subtle patterns and solid colours work best.
Try and avoid logos or slogans as they will date. In the 80's my favourite t-shirt said 'Frankie Says Relax'. It was great at the time - but would I want a photo of me wearing it on my wall today?
Avoid short sleeves and shorts unless you are happy with your arms and legs! From a photography point of view, the extra skin will again draw the viewer's eyes from the face - but also, I've never met an adult yet who is 100% happy with their bare arms and legs in a photo ;)
Newborns and Babies:
I will always advise photographing very young babies in the nude or wrapped in simple wraps (which I have a supply of). This will show off their gorgeous newborn skin and avoid their little frames being 'drowned' by clothing, resulting in the viewers' eye being detracted from baby in the finished photo. When baby is supporting him/herself better and is less likely to be swamped by clothing and for those occasions when you want baby dressed, (e.g. for a family group photo) I'd suggest keeping it simple - white and pastels are good choices, avoid bright colours and patterns.
Children traditionally look good in all white - it helps toward a classic portrait signifying the innocence of childhood. If that doesn't appeal and whilst I'd still advise avoiding loud patterns and logos - the 'avoid bold colours' rule for adults and newborns/babies doesn't necessarily apply to children. Vivid colours, especially the primary colours (red blue and yellow) can result in a lively, fun portrait.
Try and coordinate the outfits so that they complement each other. I don't mean you should all turn up in matching outfits (unless you really want to of course and jeans and white tops for an informal family group is always nice). Choosing clothes in different shades of the same colour or similar, complimentary colours will help. I like the photo below because of the complimentary colours - I don't think it matters that granddad is wearing stripes on this occasion! On a side note, I met this lovely family again a while back - the children are all very much young adults now!