Both of my kids have Asthma so I am super worried before a trip. I don't pull them out of school early through because the incubation period for most germs is 1-3 days but then you need 1-3 days for the meds to work if needed so now you are up to a week and you haven't even left yet.
Both of my kids inevitabley get sick when we are away, probably from some little sick kid who rode a ride right before they got on. In an effort to keep things controlable I keep the kids away from hot spots like Chuck E. Cheese & play dates the week before we go. I always bring my kids in for a check-up 3 days before we leave and tell my Dr. where we are going to be (WDW of course). I make sure I get the name of a pharmacy that will deliver to my hotel and put it in my cell before I leave. I always pack kids Motrin, Sudafed, pepto Bismal and keep the Motrin in my purse in addition to all the Asthma stuff that is ALWAYS there anyway. Then there is the all important Purell and wipes to wipe down every eating surface and all hands after getting on a ride. The bigger issue is that this stuff can't always be avoided but with a little TLC & management you can all still have a nice trip.
Some years my kids have gotten get ear-infections and we've either been to 'Urgent Care centers' or the Dr calls in a prescription t/b delivered and we're fine when we leave. One year I asked the DR for a perscription for antibiotics because someone else in my home had strep and it will probably spread,which it did. Our Dr wrote it out with instructions not to use it unless the fever comes, it came and I was prepared. Last year it was Croupe.
What can I do? Since Florida isn't too cold & I know it isn't too serious due to the check-up before departure I usually follow the Dr's orders. Usually this involved treating with Motrin (or whatever), wait until my child is feeling better and then have a slow kind of day watching parades , seeing a movie, going to the shows & resting frequently.
I don't think we've had an illness completely ruin a trip since my kids were 3 & 4...BTW this was the year before I started my traditional pre-vacation check-up. The $40 co-pay for both kids is well worth saving all the $ I am spending on my trip, I see it as a form of Insurance so I budget for the office visit like I budget for everything else.
Not everyone will agree with my methods but, then again, not everyone has Asthmatic kids and even those that do might be more inclined to 'see what happens' than I am.
In the end do whatever makes you feel comfortable & have a great time.