Trying to remember the name of a book I read in the mid-to-late eighties.
A father brings home an experimental computer game. I remember the game was 8-bit type 2D, may have been level based.
Of the kids, the older brother is somehow pulled into the game, and has to avoid the games monster in order to survive. His younger brother and a friend (friend may be a girl?) try to save him.
At some point they're all in the game, and everything is 2D.
I remember the cover had these blocky-looking black game monsters.