This seems to have some parallels from FNaF, which I find interesting. All the kids who are now dolls were forced in by the joker, who now uses them as an exhibition of sorrows.
Spoilers from here:
I feel like Kid1 died because of lung issues. In the drawing wherein we inflate the hell out of him, his lungs seem to be destroyed. Either he succumbed to some lung issue, or the clown lured him in and pumped helium (well, industrial air pump) onto his lungs so much that he died from that and then became a puppet. He did like balloons so he got inflated up like that in some sick, sadistic way.
As for the faucet man, I don't know his death much besides probably faucet impaling him. Could be a premeditated murder of some sort, with the clown deliberately loosening up the screws in his house. He liked being clean, so I guess clown did it by making sure he is still in a tub of water. I like to think that he has no idea he even died.
I feel like gloves would be either a father who loves his kids very much and was there to help them, an employee in some circus for which the clown was working, or another child who liked to help others of some sort. He looks very encouraging and supportive, which is why I have the vibes of him being an older person (or maybe he's just some sort of an elder sibling). Probably died because the clown took him finger by finger and he somehow bled to death that way.
Stretchy girl seems to be the curious kid who was very excited to go there but the clown basically forced her to come with him. When she refused, he dragged her hand and therefore she stretches. (Or I guess she was stretching out for her parents which makes it look like that)
Jack in Box was probably a ruthless sort of killer imo, either some sort of psycho kid or clown's fellow worker who accepted this.
All these kids were definitely alive as we were torturing them (balloon kid expressed stuff and even if they all had facial expressions, it seemed authentic when he gave sounds) and wilting of flowers were probably some sort of representation of how their innocence faded away (or time passed, alternatively...or, I guess, just how dark their future was afterwards).
Given the red keys are to represent blood (and to an extent, death?) I assume the clown died and we reactivated him by honking his nose. The ending he threw us is probably wherein he made us like one of them, but I wish we got a small additional cutscene about opening our eyes, seeing kid(s) in front of us, it going dark and have those kids either turned or torturing us / activating us in some way. Either ways, cool concept, would like to know about MC more.