Lots of breeders use different ways - I personally find it much easier and quicker to confine mum and babies to a small room (bathroom, utility, kitten pen) until the babies have mastered the litter tray. I use the base of a covered litter box for them as my girls are "diggers" ... They can cover the entire floor with litter in their quest to dig the perfect hole. Using a litter box base means that there are 3 higher sides to contain the litter and one low side which is a perfect height for the kittens to get in and out.

You need to be very quick at "poo picking" the litter tray as many cats/kittens would refuse to use a dirty tray. I find myself picking poo 4-5 times a day and replacing the entire litter daily. In an ideal world, I'd be using 2 or 3 kitten trays instead of the one larger tray but unfortunately, my girls insist on emptying them first.