I was at school in the 1970s and 1980s - asthmatic, hay fever sufferer, covered in eczema.
You would have noticed me if you were at school with me - I was the one who shook (anyone had Ventolin syrup in the days before Ventolin inhalers became common? Horrible stuff, worked OK but made you shake), couldn't run in games and for several years was bandaged up for the day each morning before leaving for school, after that day's 'bath' in medicinal olive oil after removing the previous day's blood-encrusted.bandages
Tbh I think because treatment was much less good - Piriton for allergies, Ventiolin medicine for asthma (I eventually had a 'Spinhaler' which was some kind of preventative treatment with sodium chromoglycate, which revolutionised my life), greasy hydrocortisone and the aforementioned olive oil for eczema - there was no great push to diagnose it, and there was a lot more 'just living with a cough and a wheeze'. I missed a lot of school, particularly in the summer, because i couldn't breathe - but that would mean that classmates wouldn't have known that that was what asthma looked like IYSWIM?
My father had eczema as well, though asthma not so much - but in his case he was just told it was better than having polio like his dad so he should just get on with it...
I suppose what I'm saying is that it may well have been that children did cough and wheeze and get runny eyes and itchy skin - but that the diagnosis only happened at a much higher level, when it limited what you could do to a significant extent. My siblings have been diagnosed with eczema in adulthood, but weren't diagnosed as children because 'it's not that bad'.