Hi, it's probably due to the change in litter. Especially with kittens you need to do this very carefully as they are very sensitive to change. Most people advise mixing some old with a sprinkly of new and changing it more and more to the new over a week or so. They're probably just confused because the new litter looks/ smells / feels different so they're unsure where to "go" now. They like to have a good sniff and paw around in their litter before they go, so if it has changed it will confuse them, as will a change in location of the tray. Try going back to your old brand and introducing the new one gradually. They may resist the change, in which case, can you put up with the old brand if they don't like the new one?