my daughter was 6 when she went under a general to have a few of her molars capped (the enamel hadn’t closed properly), we bought a copy of ‘Franklin Goes to the Hospital’ and read it a lot, it’s about Franklin (the turtle) having to go in for a minor surgery procedure and how he learns that it’s okay to be worried and knowing that it’s going to be okay… we were also very honest with her, that it would be a little scary but i was going to stay as long as possible and would be there when she woke up, etc…