This article is from the Care of Orphaned Kittens FAQ, posted to rec.pets.cats newsgroup. Maintained by Sharon Talbert with numerous contributions by others.
Weigh the kitten on the first day and re-weigh and record the kitten's weight at least every other day. Use a postage scale or food scale or baby scale (the bathroom scale is not going to cut it). Observe the kitten's daily progress closely. if there is failure to thrive, weight loss, signs of distress, lassitude, or change in body temperature, consult your veterinarian at once. Be alert for changes in behavior; if a newborn kitten persistently crawls away from the nest or (in the case of a litter) seems always to be on its own, consult your veterinarian at once.