What’s their diet like op? Apparently (I only heard this on the radio a while back) a lot of the body’s immune system is in the gut? Are they eating a wide variety of different coloured fruit and veg for example? Are they eating too much beige food?
Have there been any threadworm infestations at the school? Apparently Ovex or equivalent can destroy the good bacteria in your gut as well as the parasites. I should add that I’ve no personal experience of this so don’t know for sure, but a fellow parent mentioned it. And I saw it mentioned on here too.
Is there a possibility you are using too much bleach or disinfectant at home so they haven’t built up resistance?
Are they eating school dinners? What are the hygiene practices like in the school kitchen?
Have you ever visited one of the school lavatories out of hours during a parents evening for example? I did this because our dds were all avoiding drinking at school, because they didn’t want to pee and be forced to use the horrible loos. Is there running water? Enough hand towels?
Is there a bullying problem at the school so your dc are either nor daring to go to the loo, or are they stressed for that or any other reason?
Are your dc getting enough sleep?
I don’t think you can do much with the school except join the PA and lobby the powers that be to look in to the matter? We lobbied our head teacher to upgrade the school lavatories after the pandemic.
Presumably if many dc are having lots of time off and damaging attendance records then it soon becomes their problem too? Have you talked to other parents to see if they are experiencing lots of vomiting bugs too?
Other than that, you might just have vomity dc! All dc are different and some do vomit every time they get a temperature and others not so much?
Good luck, I hope you get to the bottom of it. You never know, it might just be post-pandemic lack of immunity and you are over the worst now!