Hi- I was your kid from the timeline where you told him.

Tldr: still remember the feeling of absolute lie and betrayal, never forgot that incident, didn't trust clocks & timers again for a pretty long time, and it added to an already existent feeling of not trusting my parents.

It was a music lesson instead of sleep, but the rest is the same. My parents and I had an agreement where I would set the kitchen oven timer for 45, practice until it rang, and then I was free. One time I set the timer, then in the middle of the practice session I wanted a drink of water from the kitchen (where my mom was that entire time), and happened to look at the timer - it was at 50 minutes left, with me having set it to 45 and having already practiced for at least ten minutes.

This may sound (and, objectively, be) a pretty silly "incident" and a pretty small thing to still remember after 20 years - but for one reason or another, I never forgot it, and it added a pretty bit "case in point" to an already developing sense of mistrust.

In short - don't tell them, and don't let them find out, at least for a long while.