My MiL was a reception class teacher. She retired in 1976.She taught in a small town in Buckinghamshire. She used to talk about children coming to school who had so little vocbaulary they could barely communicate. In her words, they had been talked at, talked over and talked through but never talked to.
She talked of them being unable to recognise shapes, understand words like under, over, between. They had never held a pencil or seen a book.
This, I would remind you was 1950's-1970s. So this unpreparedness for school is nothing new - and nowadays many children starting school are much younger than they were in the 1950s-70s, when you started school the term after you were 5, not the start of the (school) year you were 5.
She too sometimes had children start school in nappies, but, yes, that is a modern problem. But, as, I have said, children start school at a younger age than they used to.