Sounds like what we had
it just kept coming back
I open the house right up whenever possible. Even if it meant all of us sitting in one room to keep warm while the rest aired out etc
Burn eucalyptus oil to kill airborne germs.
Spray every surface that's germy (eg toilet seat, door handle, light switch, bathroom taps etc) with glen20 or eucalyptus spray.
Use towels once. Swap hand towels for paper towel just til you're better.
No sharing cups, plates, cutlery. Perhaps using them once, or switch to disposable.
Use gloves & wash well after cleaning up vomit, nappies etc (& try not to breath in the air while you're cleaning lol)
Take pro biotics, multi vitamins, vitC & D and garlic tablets.
Eat lots of fruit & veg, garlic etc
And rest rest rest. Keep doing the above for a week after everyone seems better, JIC. Hang in there, it was horrible