Story and how the opening sets it up

Our thriller is very simple, it is about a young girl who is baby sitting her little cousin for the day. All is going well until Olivia gets a phone call from a friend. she looses her concentration and stops paying attention to Amelia, when she turns around after her phone call Amelia is not there and all which is left is the ball which they were just playing with. At first Olivia thinks Amelia may be hiding from her, but after a few short seconds she realises this is not a joke and Amelia has gone. she frantically runs around looking for her, but cannot see her anywhere, she finds a dummy on the floor with Amelia's initials on it, this is when it all becomes real. After this more children start to go missing, but no one seems to be able to solve what is happening. There are no clues to what is happening, people have been questioned and places have been searched and yet nothing. People are starting to believe that anything is possible and nothing is beyond belief.