I don’t have children, but I know of a hack that I use to get my numbers on my smartwatch, and it might be a bit complicated, but I imagine there are people here that can help you get set up with other systems. It’s not entirely new - I’ve had my numbers via a smartwatch for years - but I love having my numbers visible on my smartwatch, and definitely keep me in range.
In a thread, we discussed how to get to see our GCM numbers on our smartwatches running Wear OS 3. Dexcom hasn’t updated its app, but there is a way to use one app that can get the numbers from Dexcom and another app that allows those numbers to be displayed in watch complications (small inner dials). You would subscribe to your child’s Dexcom account in one app, then use another app to get that onto the phone, and that would also allow you to see the numbers on the watch face.