Stomach bug? Help!

[BR1007]

I'm writing this thread to see if anyone has any ideas...because I'm so confused! Lol
DD (2 years old) started with diarrhoea 6 days ago, and started vomiting 2 days later. She's back to her normal self now but last night, DS (4 years old) started vomiting suddenly in the night.
Now I know it sounds like your normal tummy bug...but the fact that he started with it 5 days after DD did has totally thrown me and has me wondering if it could be something else?
At least 7 adults have been in close contact with them (and been vomited on, multiple times) over the past week and have not started with any symptoms at all?
No matter what you read and our GP, have said stomach bugs start between 12-48 hours after the person is exposed to the virus, hence my confusion! 😂
Has anyone else experienced anything like this?

Adults can have immunity, noro can stick around on surfaces for a week or longer. so it all makes sense to me.

As PP said, adults have immunity to lots of children's bugs or we would be ill as often as them. It's likely to be the same bug but it also may be something else your son has picked up at school/nursery, less likely though.

It could be food poisoining. You can get that a long timd after eating sonethibg.