The thing is, within normal, stable households, most of good hygiene practices - including hand-washing after using the restroom - are unnecessary. You already share all the microflora, and if one person brings in something contagious, you're gonna get exposed no matter what, and it's up to your immune system to save the day.
That said, these practices do matter in other settings shared with strangers, so reflexive habits are worth having for that reason alone.
That said, these practices do matter in other settings shared with strangers, so reflexive habits are worth having for that reason alone.