Montessori School Escape

I went to my sisters school to pick her up. I went inside her classroom in search of her but to my surprise no one was there. Thinking that she might have gone with my dad I decided to leave, but the door got locked automatically. Now I am trapped inside the class room. Can you please help me to search for the key of this room? Play Montessori School Escape and other Escape the Room games at CafeCafe Games