That's me, juggling with three kittens in a hostel in Borneo.
Not very different from juggling with balls.
The trick is to keep the kittens from spinning around, as this makes them a bit upset.
I don't recommend that you start your first juggling lesson with kittens. it's better to practice first with non-living objects, like balls, rocks, fruits etc. Then, once you can juggle well without dropping anything, you can start with kittens. And once you get good with kittens, you can juggle babies :)
Disclaimer: No kitten was hurt during the making of this photo. But I got a few scratches!
View more of my kitten juggling photos.