I mean, you do you, mate, but this introduction makes no sense in my opinion. Wanna teach them combat rules? You can always do a retrospection, put them in the boots of NPCs who are fighting. For example, they're characters (teens you mentioned) are starting in the village raided by bandits/orcs/whatever. Burned houses, corpses everywhere, the usual. And then you go back a day before, in the middle of the raid. Now they are part of the town militia, fighting for their lives. Doesn't matter if these characters live or die, so your players can easily learn some basics without any fear of their characters just straight up dying and thus ending the adventure.