The clock can certainly also be used for children.
However, only the current data is visible on the watch. To monitor heart rate and sleep quality, the watch must be synchronised with the mobile phone.
However, synchronisation can also take place only every few days.
I had the same problem: always after about 10 seconds the frequency was gone and only -.- was shown on the display.
I contacted Garmin several times until someone finally told me that the heart rate via the chest strap is only displayed during an activity that has been started. You can't find this out from the user manual either.
So: if you wear the chest strap and do not start an activity, no heart rate is sent to your device, which is in smartwatch mode. For example, if you start the activity Running, you will see the heart rate.
Personally, I find this very unfortunate, because if you want to monitor your pulse outside of an activity, the functions of the Smartwach are not available.
On the underside of the watch, 2 screws hold the straps. This makes a total of four screws and the connection for charging the watch. However, this connection is slightly recessed in the watch case. Unfortunately, I can't say what material the metal is made of.