In your MaineWash Domestic!au when was there a time that Maine was ever legitimately scared for the safety of Wash? Simra? Kellan? Nya? 'Cuz Maine is a daddy in that au, and if there's anything kids are good at, it's scaring the shit out of their parents. And Wash is a Derp so he must have done something at some point to scare Maine. (Though I imagine Maine would have been a Pouty McPoutface about it afterwards. "I said I was sorry!" "Hmm." "Please stop color-coding my socks! Talk to me!" "...")
Early on Simra has a tendency to…wander. She’s used to going where she wants, and it takes her awhile to get used to ideas like “at the aquarium I should stay where Daddy Maine and Papa Wash can see me.” There is a reason Maine will take any reason to hoist his daughter onto his shoulders or a piggy back ride when out with her, it’s because then he knows where she is. She learns, Slowly.
Wash constantly worries that they’re not doing right by Kellan. Partially because Kellan tends towards quietness and slinking off and hiding when something is Up with him. He likes flying under the radar and Wash is terrified he won’t notice something important because he’s so understated. Kellan’s teen years are rough.
The cave-in at Wash’s work scared Maine. He also has a big scare later, but I’m not going to mention it here because I’m writing it.