1) use clumping litter. It is sooo much better
2) use a cat box with a cover to it and face the opening away from you. This at least keeps the odor contained.
3) check to see if the kittens are properly covering up their poop. This is usually instinctive but they may need some demo help by you gently taking their paw and helping them to cover it up.
You shouldn’t really flush any kind of litter down the toilet, especially not clumping, unless you enjoy making regular contributions to the plumber’s kids college fund.
If you are there when they poop, you can either make sure it’s covered and the smell usually dissipates in a few minutes or you can scoop it out and put into a closed container. Smell gone.
The do sell these types of containers and liners, but I just recycle grocery bags and use an empty bucket with a tight lid. You can get a cheap five gallon bucket at a paint store.
I just keep re- using the square one in jumbo size in which the litter was purchased.
The larger litter sizes (25 lbs or so) come in real sturdy plastic buckets, the smaller ones in cardboard which obviously can’t be re-used.
If you are diligent about the scooping and baking soda, you can have a pretty odor free litterbox.
Mine is in the closet of my bedroom and others have commented that it doesn’t at all smell like cats.
Aside from the 5 mins or so immediately following the poop, mine just doesn’t smell. I scoop regularly.
Don’t forget to get them neutered when old enough. There is NOTHING WORSE than the stench of unaltered adult cat pee.
Enjoy the little darlings. They are definitely worth it.