Hey, me again. Just a quick oddly specific tip: If you're going to be writing a person turning into a child/infant/toddler for any reason at all, they're probably going to vomit blood.
An adult usually has around 1.2-1.5 gallons of blood in their body, if they're shrinking at an alarming rate some of it has to go. Character 2 has to come to Character 1 sitting in a puddle of their own blood at some point