my cat won't clean her baby

This is my cat's third littler of kittens. She has recently had an infected paw but we got that cleared up with the vet, and she's also taking this stuff to help with her being anemic. She does everything she needs to, except cleaning the kitten. I have no idea what is on the kittens backside. I checked on her one day and this like, brownish yellow lump is like, right on her backside. Is it because her momma won't clean her? I'm really scared to mess with it because i don't want to hurt her. She only has one baby, so it should get plenty of attention right? I need help!

She should be cleaning it regularly.  If she isn't you need to.  Use cotton wool & warm water, or unscented wipes.  The kitten cannot pass urine or faeces without this cleaning so if she isn't doing it the consequences can be fatal.  The kitten might cry a little and wriggle, but they do that when mum cleans them.  There shouldn't be any blood.

I moved this thread here in the hopes that more members with experience with kittens and momma cats can add their input.
I agree with OrientalSlave that you do need to clean the kitten's bottom, for the sake of hygiene and to stimulate her to have a bowel movement and to pee.

Singletons can be harder to care for. they aren't always enough to keep mum interested

If you are concerned about the kitten you can always phone the vet, they'll advise whether she needs to be seen