Oh yes I feel your pain.
I have a 5 year old at school and a 3 year old that does 2 days at preschool. Since September we have not had a day where one of us hasn't been ill. Nothing serious, no covid (numerous PCRs between the 4 of us and regular LFTs for DH and I) but coughs, colds, tummy upsets, general being run down and ill.
3 year old goes to preschool mid week, gets sick, gets better for a day or so then goes back only to get sick again. 5 year old picks it up from 3 year old (or school) and is constantly on/off low level ill. DH and I seem to take turns getting whatever they've got. One day we collected eldest from school because she'd started coughing to take her for a PCR and her teacher told me they were down to 19 children in class that day, out of 30.
I actually took my 3 year old to the GP a few weeks ago because she just couldn't shift her cough after weeks and I was concerned about a chest infection. She was fine. But GP told me they obviously they do pick up everything going at this age when they start preschool (and I remember my eldest being ill quite a bit too) but this year they are seeing an unprecedented number of 2/3 year olds who are having much more prolonged illnesses, more than normal and sicker than normal (as in, being sent to hospital because they are really poorly not just 'kid with a cold'. A result of them all being kept away from people for a large chunk of their lives probably.
Luckily I vaccinated both of mine against chicken pox as babies so at least that's one thing I don't have to worry about. It's flying around preschool at an alarming rate again and so far we have avoided it. Eldest never caught it there either despite it being rife.
Roll on the spring. I should take out shares in kids Olbas Oil, Calpol plug in refills and Vicks at this rate!!