pelorus, not all of those situations have to be resolved in combat, and again I already stated hit points do not fit every situation. Elliot's life or death Trouble could be resolved by X number of successful vs failed rolls, whereas having a fight between an NPC and a Kid that's a slugfest could benefit from a health bar for each one. As I said, these kids don't have to die, but if they're in situation where that's a possibility, why not keep it real? Also, I'd have the train scene be a roll of successful dice, too. Can't tick off HP on that. I brought up Will from ST because you mentioned that no kids were hurt in that and Barb (the only one of the group to die) was not a kid, but Will, though off camera, certainly was hurt and might even die in the next season, so if you're using that genre as a template, then the Kids in the Loop are still subject to being hurt and killed. Also, Nancy was the only person concerned about Barb. I will agree that the death was pointless and just used to show what happens to victims of the creature, but Barb's friend was anything but unphased and was the only person who was looking for her.
Also, it's not fair to shrug off horror movies of the 80s since so many of them dealt with kids, too. The Gate, Sleepaway Camp, It... all movies about kids (well, if you ignore It's scenes where the kids were grown) and with interesting plots that could be used for Loop campaigns.
I'm all about less complexity, too, but some things need a bit more to them than just a successful roll of the dice. I think the system in place works, but there needs to be something bigger for Showdowns. If not actual hit points, then some way to have a battle played out. Just allowing for 3 successes in a roll to win is kind of lame after all the build-up of the Mystery. The sample campaigns don't really go into detail about fight scenes, which it very much needs to. My thoughts on a Showdown would be.. say for instance, the Goshawk.. It's trying to hurt the kids, the kids are trying to subdue/kill it, and it's also trying to escape. It's the main boss of the Mystery, though, so there needs to be more to the encounter. I would put forth that there should be x number of successes needed each round of dice rolls and keep track of how many hit points the kids have taken off vs how many fails they have had to allow it to escape. Something along the lines of:
Goshawk has 5 hit points and a difficulty of 4. So the Kids would need 4 successes in a roll of the dice 5 times. However, a failed attack (where there were not enough successes in the roll) would give the Goshawk an escape point. Accumulating 5 escape points before the 5 hit points are gone would mean the creature flees. That is more or less what I had in mind for where hit points of some sort are useful, so that the Showdowns have some meaning to them after the buildup.
There might be some instances where the Kids would need hit points in the same manner.. such as in a fight against a bully. Whomever knocks out the other's hit point counter first with successful attacks wins the fight (because there are some things the GM should be rolling for, too). Or if the kid is doing something dangerous, but they have a skill in it, there could be a counter of unsuccessful attempts knocking off X number of tries before the Kid is hurt or has to take a Condition.
Having a D&D style HP system doesn't work for this game, but having a way to know how far one can push their Kid beyond just the Conditions is helpful for some instances of the story.
"What matters most is how well you walk through the fire." - Charles Bukowski