Swelling

One of my two 11 week old kittens has swelling in around the rectal area. The other had a bit of blood around the same area... They still are drinking lots of water and eating a their fare share of food.

If they have to go to the vet, is it ok to wait untill Saturday? This is when they will be going to recieve their boosters/test/etc..

Hmm I would think you may want to call the vet and see if you can push the vet appointment up a couple days at least. Tell them that you have an appointment next Sat but there is a problem and you would like them seen sooner if possible. You can also mention if it is something you need to worry about.

All I can think of to ask is what kind of litter are you using? You should never use scoopable/clumping litter for kittens because it tends to clump to their butts and can get the area infected. Kittens also tend to sample their litter and eating clumpable litter is not good and then trying to poop it out...I don't know, just some thoughts there. I may be off and if you are using unscoopable litter then I really have no idea.