(( I know someone asked me this question, but I can't find it anywhere in my messages, not sure why.
For those who do not know Amber, she's a Rise of the Guardians fan character. To put it simply, she's the spirit of Fall and people like her cannot be seen unless believed in. As there's no stories about Fall (least not where I am), these kids cannot see her.
Ask Amber main account: http://askamberfall.tumblr.com/
If you would like to ask Amber a question, note me with "Ask Amber" in the title. ))