Creepiest Movie Children - Rotten Tomatoes
The Orphanage (2007)

Laura, her husband, and son, Simon, have moved into the orphanage she was raised in. Laura's plans to re-open the place are put into chaos when Simon disappears at a party and she's attacked by "Tomas," Simon's supposedly imaginary friend. Who has taken Laura's son? How can Tomas really be real? Is he involved? And why does he have to wear that scary-ass sack mask? The answers may haunt to the grave.