What your son should of told you is "it is safer" than most parts of Ukraine,IMO.
Nowhere in Ukraine is "Safe",The Russians can,will and continue to strike any Region at any given moment.
As someone said earlier,shelter as soon as the siren is raised.
Ukraine monitor take off of strategic bombers and raise the alarm straight away.
Normally takes the bombers around 2 hours to get to launch zone,so plenty of time to get to a shelter.
Not that any of that will make you feel any better,just letting you know,they don't just drop out of the sky immediately.
Hope he stays safe.
Slava Ukraini.