Tenza

The Tenza were a species of alien whose young were raised by another species.

Biology
Tenza had advanced, though subconscious, psychic powers, allowing them to live among other species. They used a perception filter to remove inconsistencies in their history. One Tenza was capable of capturing people who frightened him, shrinking them down to fit in a doll house and eventually turning them into living dolls. He could also contact the Eleventh Doctor's psychic paper while he was many million of light years away. (DW: Night Terrors)

Life Cycle
Tenza are born in space, where they drift until they find a habitable world. If they find a family that they can live in, then infiltrate it. The Tenza infant will adapt itself to perfectly suit its environment and alter the surrogate parents' memory and the memories of those around them. After that the alien would try live out its life as a member of that species, without conscious realization of their true nature. These Tenza would have some odd "tics" which drew attention; for example, Alex noted that George blinked too much when he was frightened or would stare off in to space at odd times. If the Tenza felt it was threatened or likely to be removed, their telepathic abilities would start to play havoc with their environment. (DW: Night Terrors)

History
At somepoint after Claire and Alex had learned that they were unable to have children, a Tenza came to Earth and adopted them as his surrogate parents. They named him George, raised him as their own (believing he was due to the perception filter, and though considered him an odd child, they had no idea he was anything other than human.

Before he was 8, George's phobias started to develop. His parents tried to help him, but eventually decided he needed professional help. George thought this would mean he would be taken away, and this was enough to set off his psychic defences. His phobias came to life in a doll house, which was governed by the Peg Dolls who would terrorise him and abduct anyone who terrified him. He also contacted the Eleventh Doctor on his psychic paper. When the Doctor came to investigate, he eventually realised that George wasn't human. This set off George's defence, pulling both the Doctor and Alex into the doll house. When they were attacked by the Peg Dolls, the Doctor tried to get George to help them, which caused him to be pulled into the doll house and attacked by the Peg Dolls as well. When Alex saw that his son was in danger and tried to save him, it proved to George that his fear of his parents sending him away was unfounded, returning everything to normal. (DW: Night Terrors)