I would suggest Fuji Astia or Kodak Elitechrome. The elitechrome is a "consumer" level slide film that is both cheap (in comparison to Kodak's other offerings) and works very well with skin tones. These are both daylight/flash balanced films, though--will these shots be available light from the sun or artificial, because that would make a big difference.

I also liked Provia in the Fuji slide category; it gives a little more snap in the colors than Astia, but renders skin tones quite well.

I have personally shot all of the above films.