iPhone is fully unresponsive: won't charge or power on, how can I fix it?

The phone is my sons. He got in trouble we took it away. Left it on and it died on its own. Was dead for a week and when we gave it back to him it won’t charge, Turn on, light up nothing. Tried the up volume button and down volume button and hold the side button. None of the trouble shooting is working. The software fix you can do online doesn’t work because his phone won’t charge or come on. Won’t do nothing

[Re-Titled by Moderator]