David, a Mecha that resembles a human child and is programmed to display love for its owners, is sent to Henry Swinton, and his wife, Monica, as a replacement for their son, Martin, who has been placed in suspended animation until he can be cured of a rare disease. Monica warms to David and activates his imprinting protocol, causing him to have an enduring childlike love for her. David is befriended by Teddy, a robotic teddy bear, who cares for David's well-being.

Disheartened, David falls from a ledge, but is rescued by Joe using their amphibicopter. David tells Joe he saw the Blue Fairy underwater and wants to go down to meet her. Joe is captured by the authorities using an electromagnet. David and Teddy use the amphibicopter to go to the Fairy. The two become trapped when the Wonder Wheel falls on their vehicle. David asks repeatedly to be turned into a real boy until the ocean freezes and is deactivated once his power source is drained.

Two thousand years later, humans have become extinct, and Manhattan is buried under glacial ice. The Mecha have evolved into an advanced, intelligent, silicon-based form. They find David and Teddy, and discover they are original Mecha.

Monica is long gone by this time. David meets up with Monica once again only because of the newer Mecha and a piece of hair that Teddy had saved earlier in the movie and is needed to bring Monica back but only for 1 day. David as well as Monica enjoy thier last day together as Mother and Son.

More Info: en.wikipedia.org