My Parents Are Aliens was an ITV series that ran for 8 seasons (106 episodes) between 1999-2006. It follows three orphaned children: Mel (Danielle McCormack), Josh (Alex Kew) and Lucy Barker (Charlotte Francis), and their new foster parents Brian (Tony Gardner) and Sophie Johnson (originally played by Barbara Durkin and then by Carla Mendonça).
The problem is their foster parents are actually aliens from the planet Valux, who crash-landed on Earth when Brian tampered with the controls of their spaceship. As shown by the opening credits, the house they live in is actually a morphed form of their spaceship. They also have the ability to morph into other people.
Brian and Sophie start out with a very limited and muddled knowledge of life on Earth, and the children must do their best to help them acclimatise. No one outside the family must ever learn that they are aliens, or they will be taken away for scientific testing, and the Barkers will lose another set of parents.