Reassurance from an older mother, with DD's now late teens.
We got everything when they went to nursery/pre-school. A couple of years of coughs, colds, chicken pox, tummy upsets, sickness. They got it, and we caught it too.
However, since then, so all through primary, and secondary, and university, pretty much nothing, for any of us. Really strong immune system. Not one of us has had a sickness bug in 15 odd years, no flu, odd cough and cold, but nothing terrible. DD's both got freshers flu at uni, but that's normal too.
Oh, they did of course have the usual nits and worms in primary, but again, only once each, and DH and I didn't get them (that we know of!!).
So, hang in there. It really does get better, and being exposed to all these bugs when they are young, is actually a very good thing.