You'll Like It Here (Everybody Does)

While Meggie and David Blue are from another planet, they're a lot like Earth kids, with similar hopes and dreams, and can't wait to grow up. BUT they also have GROSSLY UNIQUE qualities, such as blue streaks in their hair that pop up randomly and language skills that sound like nothing on this planet. The story takes these alien kids, along with their mother and grandfather, by accident, to a far planet in which the society is not only oppressive but hostile to individual freedom.
People are kept submissive through drugs and brainwashing. The Blues, who have spent time in free societies recognize the upside-down-ness of this world. They're almost helpless to do anything, but do what they can, plan their escape, and vow to help others.