Mama cat did not teach kittens to use litter tray

The mama cat has not taught the kittens to use the litter tray. I did introduce the liiter pan early enough but they refuse to use it. They just pee or poo in the corner or under the table. What can I do??? Should I have litter trays in all the areas they pee or poo?

If there is a piece of paper on the floor, they will go on that.

Confine everyone in one room - like a bathroom. Does the mother use the pan? If so, the kittens will copy her. Maybe they don't see her using it?

Also you need a shallow pan for the kittens when young till they are big enough to climb up in a normal litter pan. That may be the reason they won't/can't use it.

How old are these kittens?

You know the little shallow foil brownie pans with clear lids? I used the lids as a litter pan for tiny ones.