I suppose prosecutorial discretion is the only solution. Biased/unreliable as it may be.

On the technology side, I'm thinking of two bluetooth (or similar) enabled wrist bands. One for the kid and one for the mom/dad. When the device loses connection to the other, the parent's band beeps and must be manually silenced. The kid's band could be connected with the car via bluetooth so the only time the alarm can be activated is when the kid's wrist band has been connected with the car in the last 10ish minutes (adjustable). Though if I were a parent I'd be worried about losing a kid in general too.