Have 4 week old kittens and their mother doesn't use a litter tray, she goes outside. I put a litter tray in when she was giving birth incase she wanted to use it instead of leaving the kitty's but she never did. She kept going outside. My question is, will she teach the kitty's to use it? I have noticed the blankets are wet a lot now so they are not using it at the moment. What should I do? Thanks in advance for any advice.