I am leery of people who are "good with kids" and seem to easily build a rapport with young people. The are smart, like you say it will be someone you trust. And how does one gain trust? Buy being NICE, and polite, and good with kids. They are able to put themselves in a position where children are easily accessible. I have never trusted anyone with my kids. I never left them with a sitter. I took them everywhere with me, and if they couldn't come with me and my husband was not home then I simply did not go.