Don't panic if a kitten fails to have a bowel movement. Each kitten is different and some do not go every day. Diarrhea is a more common and serious problem. At the first sign of the runs, dilute the formula just a little. If there is no improvement by the next day, see your veterinarian immediately.
Kittens dehydrate very quickly.
Therefore, the kittens' weight should be monitored daily. Pull the skin up. It should go back down pretty quick. If it doesn't, he probably needs fluids. A warm, slightly damp washcloth gives a comforting bath to the kittens.