We're currently fostering a mum cat and 3 adorable kittens. Two of the kittens will not litter train. I am regularly putting them in the litter, it's in a good position, designed for kittens. A week and a half in they are still toileting anywhere but the litter - in their bed, in their toys, on us, just in the middle of the floor. The floor is easy clean but they are not improving at all. We've tried penning them but it makes them so miserable and they still just toilet in their bed. They are noticeably less affectionate.
They can't be rehomed until they are litter trained. Any tips would be welcome. I've fostered cats for years but this is only our third set of kittens and the others mum did the litter training.