I read on forums all the time about some folks want to make an adventure a Total Party Kill or not. Some seem to revel in. Others are a bit averse.
Myself, especially as a DM/GM for kids, I don't hold the TPK very highly. I think that first off, this is a game. Games are meant to have fun and be a bit of escapism.There are plenty of things in realty that show us the grim reality of life. TV news, First Person Shooter type games, and so on.
I happen to think the game I run is more fun because it appeals to the "Hero" inside of us. Sometimes even the "Arch-Villain" inside of us. It's an outlet to put one's imagination into action.
I don't write the adventures I have my kids play in with the intention of "me vs them" or even geared to outright attack the PC's from the moment the game starts. I start with a mission. Almost like writing a story or an outline of a story really, Then I leave a lot of room for random encounters. It's the random encounters that really make it a challenge. But random encounters don't necessarily have to be rolled out on the tables.
This is where the DM's creativity gets to shine. Perhaps a thief that was allowed to escape earlier gets a chance to follow them and try to pick off the party's goods in the night? Maybe an unplanned ally is introduced.
My position is to always give the party/PC an out. Maybe they don't take it, but it's there. Then they have no one to blame but themselves if someone dies. The point is, I'd rather give them a chance to succeed instead of ensuring they all die.
So, is it possible for a TPK in my games? Well, yes, but, I always leave an out and I try to make sure they have a chance to succeed. I'm not above throwing in a little Deux Ex Machina if it helps the overall game.