The mother cat licks the derrier and stomach of the kitten to stimulate
bowel movements.

But I don't know at what age that stops.


Here is one resource:
http://www.allsands.com/pets/cats/or...ten_squ_gn.htm

http://www.our-happy-cat.com/help-ki...-bathroom.html

I'd make sure this kitten is getting enough water and fluids.

I had a neighbor once who got a very young kitten from the Humane Society...less than 8 wks. They neuter them that early now. Was yours neutered? This kitten was bleeding from the rectum and had to be put down. (the surgery damaged it).
It is a very sad story. I remember the cries, and they were really awful.

I hope this resolves for your new kitten.