muse a & b are neighbors. a is a single parent (for whatever reason) and b just wants sleep. b goes over to a's house (next door or across the hall) and they offer a help bc they have a nephew/niece and know this stuff. a is skeptic about it all but gives in anyway due to exhaustion. muse b holds the child and a watches them to make sure b isn't kidnapping their baby or something, b notices and says it's fine. muse b convinces muse a to shower or something. an hour later muse a wakes up from an accidental nap and muse b is sleeping with child. muse a won't wake b up so the child doesn't wake up but also because b actually looks really peaceful.

muse a asks b if they can babysit later because they need an extra shift at work and b isn't so sure but does anyway as long as that means keeping the child quiet. but b and child end up getting along and bonding (depending on age)

bonus: someone sees muse b with child and assumes they are dating and they should totally come over together with the child. one of those "oh nonsense, you're not a burden. you're coming over for diner and it's final. see you later" type of invites.