Do you have headcanons on how the other five kids died? (Aka the ones besides chara and clover) Or just headcanons in general
We know, through environmental context clues, where the five children could've died in where you find their items. I assume those children died somewhere close to when they discarded their items
We know that the children fell after Toriel left the castle and went into hiding in the ruins. We also know that until Frisk fell, monsters hadn't seen a human in a long time. Most monsters you interact with don't notice you're a human, so monsters like Undyne or the other gaurds may not have even encountered a human before.
Patience's Soul most likely died just after leaving the ruins. They wanted to leave and so patiently waited until Toriel was not looking before leaving the ruins, only to meet their end in Snowdin.
Bravery's Soul fought back and died in Snowdin, and their items were subsequently found by the shopkeeper.
Integrity's Soul tried hiding in the tall grass in waterfall, shedding their ballet clothes maybe as a distraction, but ultimately got caught.
Perseverance's Soul persisted all the way until the near end of waterfall, succumbing to injuries.
Kindness's soul managed to get through the underground with kindness, until a royal guard stopped them in Hotland, unable to be swayed by their kind words.
Justice's soul would the one to make it the furthest. I'm very married to Undertale Yellow's pacifist version of events.
Monster Frisk! I think they would be a light/angel monster, given their connection to determination, the save point, and the prophecy. It would also contrast with monster Chara having a dark/demon theme.