There are no hard and fast rules, however, avoid garish colors
and loud prints. Neutral tones such as black, brown, white,
cream, navy, burgundy and beige will not be tiring to the
eye. However, that does not mean you can't wear yellow, pink
or other colors colors convey moods, so think about
the mood you'd like. Also, choosing clothes with a classic
style will insure that your portrait will not later look dated.
Consider your lifestyle and where the portrait will hang in
making the choice of a formal or informal look. Though outdoor
portraits are normally considered less formal, there are some
that are actually quite formal. Conversely, an indoor portrait
could be quite casual. It's a combination of factors, including
the clothing, setting and character of the subject.
Strasburg clothes have long been very popular for children's
portraits. You can check out some of their selections at
Strasburg Children. Here are a few samples of their clothing.
Some other online places to look for children's clothing
Lads, Rags Land
Anichini. However, there are many other online children's
clothing sites on the web.