You might consider a device called a "Noise Gate." They are used to withhold ambient noise, just as you will need to do. You have heard one, in operation, and didn't even know it... Any time you are talking with a customer service type person, on the telephone. Listen closely and, as they speak, to initiate an open mic, you can hear the other CSR's yakking away... The sound must reach a preset volume, before the gate opens and the sound is processed.
They are a common feature, on walkie talkies, too. Sometimes this setting is labeled something like "sensitivity."
Google "VOX," too.
If you are developing a game, where the winner is the kid that can withstand the loudest noise, you may want to rethink that. I was a sound engineer. You can do permanent ear damage, instantly. A kid with hearing loss, for a lifetime, would make a juicy lawsuit.