hmmmm. good question because I think we all encounter this at one point or another.... so this is very universal.
For me, personally, there were no tricks..... from very early on there was just an overall "unless you are dead you go to work/school" attitude in our house. I think to the point that it was probably UNHEALTHY. It is only now that I am working in a cubicle environment that I really *stay home* if I'm sick. And that's only because I've seen the rapid fire spread of illness cross cubicle and it's not pretty.
I digress.......
Anyway, from a very early age when my daughter was sick.... it was not *fun* to stay home. If you were sick enough to stay home you were in bed. no movies, no TV. BED. That worked for my kid, because she liked to be active so being forced to stay in bed was a killer for her.
Staying home because you don't "feel well" wasn't an option. There has to be concrete evidence of illness. Vomiting. Bad diarrhea. a temp over 100. Framing those boundaries early I think is helpful.
I also don't think I ever approached school as something that was supposed to be *fun*. I approached it as on the same level as my job. This is what mommy does. This is what daughter does. Pieces of it are fun. Pieces of it are work. Pieces of it are NO FUN. But it all has to be done.
She also went to a Montessori school until 6th grade, so that is a whole different attitude about school. Which I think is quite helpful.
Now, I only had the one kid.... so I never had to deal with the envy that would come from one kid getting attention due to illness. I can see where that would be a tougher row to hoe.