First of all op, don't panic.
I'm going to bore you now but I hope some of what I say might be helpful.
About ten years ago, we used sub levels to assess children. So you had level 123 etc and within that sub levels so a 1a was better than a 1c, as it was nearly a 2. This meant in parents evening you could tell a parent while their child is not yet expected they were very close. Eg. A 2A is expected and as your child is 2b we're doing xyz and you can do ABC and they'll probably catch up. It also meant you could give an idea if the child was really behind and would help explain why we might do further assessment, strategies, Sen etc.
Anyway, that's all gone now(I clung to it like Rose to the door in Titanic, but the powers that be know best)
So what your left is a system that lacks nuance, so you need to ask specifically what's missing/needed to know how far behind and how much you need to push(the school, not the children).
It's wonderful that you are invested in your children's learning but 45 minutes of writing is way too much. At home, with your younger child, a wet paint brush(just water) outside, chalks or child led writing is fine. Phonics games and reading fine.
For your older child really try and find their niche in reading. Comics, internet encyclopedia, fiction. Whatever. If they are inspired by writing they are more likely to want to write and children pick up a huge amount of vocabulary from reading.
And that can be shared reading too, you can enjoy books together and it's still more honestly valuable than educational games.
And just to finish my little monologue, when I saw this post I immediately thought of every single child who I've had to speak to about progress. If the parents were engaged, I have no doubt that those children went on to flourish. In fact, I can recall those children's strengths so vividly and even though they may not have turned out academic, I'd be surprised if they weren't happy and successful.
But a lot of them caught up anyway, so don't write them off as non academic either.
I know it is worrying, but seek clarity and practical advice. X