The little ones will be fine.
My son is Y2. They've been particularly badly affected.
Its stuff like not being able to sit and concerntrate for more than 5 minutes. Most kids would learn it through reception and year 1, but because they haven't had the time in school many haven't. Thats causing disruptive behaviour which is affecting all the kids in the class. Too much screen time with apps which feed short attention spans doesn't help.
They also have many who are massively behind where they should be for reading. That has an affect on all the other subjects because if you can't read enough by a certain point it makes teaching harder. That again affects the whole class.
Its stuff like not being able to have swimming lessons.
Its stuff like not having social skills which are up to what would normally be expected.
Its stuff like handwriting being far behind where it should be because they've not had as much practice compared to a normal year.
After school its noticable how much more 'wild' certain years are compared with previous years and its a direct result of lockdowns. They just aren't as disciplined in the same way outside the home.
This is happening even in the better schools. Its noticable and being replicated across the country.
So yeah 6 and 7 year olds are little but still absoluetely stuffed.
Meanwhile toddlers aren't as advanced in terms of their language development as a result of not being as exposed to people generally.