Years ago, a neighbor moved in next door. Her son was 12 years old, and he was big for his age. His playmates of choice were the 5 - 6 year olds in the neighborhood. Something about him always made me uneasy. At the age of 16 he was convicted of raping his 5 year old cousin.
Not that I am accusing this girl of that, but I know that uneasy feeling.
POD to the above. I have a 3rd cousin who lived briefly with my brother's family. This was a boy of 10-11 years old, who while jumping on a trampoline with my 2 year old nephew, just had to keep hold of my nephew. I told him repeatedly to stop and eventually removed my nephew from the situation. A year or so later, he molested a little girl at his after school program. No remorse for what he did to the little girl.
Always listen to your gut.