"Ho ho ho! I'm sorry but our time is up. If you'd like to keep talking to me, please provide a credit card number. Merry christmas!"
No idea how you'd monetize that, though.
Somehow this device fits well with the Don't be a sucker video linked to elsewhere on this here site [1]. Good advice, valid in many contexts. Don't.
Perhaps a parent commitment that if the kids earn X many goodie (goody?) points, then the CC is charged, and let the parent control how they earn those X points.
Gamifying good behavior has been shown to be pretty effective with kids. See Kadzin.