Kindle Unlimited for Kids

Hi there ! So I’m 25 but I have a 9 year old sister who loves to read, I don’t have kids of my own so I’m just wondering if there are any parents/other relatives of kids on here that could help. I would love to get her a kindle and encourage her to keep reading but I’m wondering if there is a kindle unlimited option for kids, that doesn’t have them accessing inappropriate content for their age group ? Maybe if I could even somehow add her to my own subscription but limit her access ? Or would it be safer to just keep purchasing her physical books until she’s at a later stage ?