I really feel for you as I could have written your first paragraph!
It's just my luck as well that both myself and eldest DC are particularly prone to catching them. Eldest DC has had no less than 9 since he started school four years ago.
Just want to say though that it's not inevitable, nor that it will go around the whole house if you're very very careful with quarantine/cleaning/have more than one toilet (this last one is key, I think)
In fact, touch wood, none of the rest of the family caught any of the 9 DC1 has had in last few years (DC2 had one on another occasion, as did I 🤢, but again, not spread to anyone else).
The important thing I've found is for the infected person to try and use a toilet, rather than bowl, to keep it contained. DC1 is very good at knowing when he will be sick, due to experience 😅 With DC, I then clean it with bleach every single time, as well as the sink, taps, flush, surrounding floor, door handles, etc whilst wearing a mask and gloves. (I actually keep a mask on all the time I'm around them 🫣) I keep DC away from other DC and DH, and only the sick DC will use 'their' toilet for two days afterwards, after which I will then give it another big clean.
When I had a sick bug recently, I quarantined myself in bedroom for two days (felt so ill anyway, I was just in bed the whole time), but luckily have an ensuite. Got DH to leave supplies outside the door.
It might sound extreme, but the effects of 10+ sickness bugs going around the whole house in a few years doesn't even bear thinking about! The DC mostly bounce back within a few hours, but every time I've had one, I feel awful for up to a week afterwards. Even after the sickness subsides, my whole body (especially my back) is in so much pain for a day afterwards, then takes about a week for me to be able to eat anything other than a bit of toast.
Hope you manage to avoid this one. Recommend keeping masks at school for clean-up duty!