With regards to children with disabilities - I think more children would have died at birth (ds probably would have) more children with additional needs would be at special school (I used to volunteer at a special school in my teens - so early 80s - a lot of the children there would now be in mainstream) and a lot of children would just have been thought to be clumsy/odd/naughty.....
I think some conditions like coeliacs, asthma, eczema and allergies were not talked about as openly and were almost seen as a bit shameful. My cousin had coeliacs and my aunty used to do that 'hushed voice, eyes down thing' as though it was a dirty word - my 8 year old self was massively jealous of her because she got special wafers at church and missed a lot of school. Again I think because schools had no things like care plans to deal with medical needs, children with allergies etc would miss a lot of school and there would have been less visible support for children who did have these issues.
My pe teacher at school regularly mocked my asthma at school and joined the kids in calling me my friend who both had eczema 'scabby hazey and scabby ' If I needed my inhaler it was like a walk of wheezy shame while the pe teacher told everyone they would have to wait with much sighing and eyerolling.
I am sure there is a rise in certain allergies due to environmental factors - catalytic converters have supposed to have contributed to a rise in lung problems in children as toxins are released at street level. However the band with of certain diagnoses has been expanded too - more children have inhalers because ventolin is used to treat a variety of short term breathing problems and coughs, whereas in the past ventolin was pretty much only used by people with asthma.
it is in parents and medical professionals interests to invent a syndrome that gives them more help/earn more money. I am afraid I think this is bollocks, and I would love to know more about these money spinning syndromes.