A series of young adult books I read as a child in the 90s.
The basic storyline, I think, is that Earth came under attack by alien ships that feed off our photon cannons, and they steal a family, possibly a ruling family. They also steal the sun. The children who were taken away are made to grow rapidly, and they are put in a machine that downloads knowledge into their brain, making them learn fast. I vaguely remember one of the main characters being named Nova.
I remember them being quite thin books. One cover was one of the humans having an American football style helmet with spikes on it.