The Handicap Ledger
Playing a child who is still learning? Don't lose on purpose: children can tell, and a thrown game teaches nothing. Give a head start instead, and play your best. Aim for a game either of you could win.
When they win, make the head start a little smaller next time. This page can keep a note of each game so you both see it come down. The note is off until you turn it on, it stays on this device, and nothing is sent anywhere.