I unfortunately had to let my kittens go to another fosterer as my original two really hated them. They were hiding away and really unhappy. The new two who were litter trained before I had them were going to the toilet on the floor and in their beds. If I was offering them :(a permanent home I'd have tried much harder to get them settled but it seemed silly to put them all through so much stress just for a few weeks as hopefully they will find a new home soon.
I've decided to keep my original two as it's pretty unlikely they will find homes, the centre has 50 kittens at the moment.