I read this about 3 years ago, around 2017, I think as an EBook. The protagonist is an adolescent, not quite a teenager, who has moved to a small town. I think the town itself is in a valley. I do remember that it has a bridge over a large expanse of water. He's being bullied by a pair of boys who mysteriously back off from another kid, smaller than them. I think he also makes friends with a girl who's a bit socially awkward. The bullying culminates with an incident at the local observatory where he gets chased to an upper floor, which is under construction, and accidentally gets knocked off of the edge of a long drop, maybe down a cliff face. On the way down, he's caught by the kid who'd been driving off the bullies before, who can apparently fly. Bit by bit, he learns that kids in town gain superpowers, which run down the usual gamut of flight, super-strength, invisibility, etc, but that they mysteriously lose their powers, and all memories of having powers, when they become teenagers. There's a tradition of decades of the kids having a treehouse in the woods where they can use their powers without fear of discovery, said treehouse also containing the closest thing they have to an explanation, a run of comic books based off of a local frontier hero. The stories they pass down is that the power comes from the same source as this superhero, and may be taken away by his adversary, who had a name like The Shroud or The Shadow.
As an outsider, the kids take the protagonist into their trust, thinking he may have the best chance to figure out why they're losing their powers. I remember a scene where he has a sleepover with a kid about to turn thirteen, and encounters a wraithlike figure with glowing eyes, causing him to fall off of a trellis and miss his friend losing their powers. Eventually, they do track down the reason why the powers are being removed, which has ties to a meteorite at a closed-down mine in the woods. The comic books are also relevant, as they were written by the guy who's stealing the powers. I don't remember if he actually knew the superhero in question, but he has access to a part of the meteorite, giving him the ability to steal the powers, I think out of jealousy that kids have powers, and because by stealing them, he can have his own measure of power. He might have had ties with a group of orphans that the local town hero was famed for rescuing from a fire. During the confrontation, the protagonist learns that he too might be able to use the meteorite shard to steal his own powers.
Other things I randomly remember was that one kid had extremely heightened senses that he had trouble turning off, one girl had the power of invisibility (I think she was hinted to have a crush on the protagonist), and there was a boy with the power to manipulate electricity, which had the side effect of making his hair always stick out. Oh, and there's a scene where they save a lady who drives off of the bridge, with I think a hint that the town's residents know that kids have superpowers but keep it under their hats.
I'm pretty sure there was a sequel where the main character starts accidentally stealing powers, I think after a scene where the kids are doing spectacular jumps from the bridge to the water, knowing their powers were keeping them from getting hurt. The girl with invisibility, I think, asks him to take her powers away permanently because she just wants to be normal. And, unfortunately, that's all I remember there.
I want to say that the title was a single word, like "Heroes", and that the cover was done in a crude drawing style, like a kid drawing a superhero with crayons. I don't think the books had anything terribly adult in them, other than the vague peril, so it might have been a YA book.