It really does boil down to a change in attitude as many PP have said.
Our children are not in solitary confinement - that's a ridiculous term to use. Everyone can go out for exercise, even a walk up the high street is exercise if you can't go to a park. Have a look at the shop windows, choose your favourite, have a chat about why whilst you walk. Have an 'if I won the lottery I'd buy that house' type walk around the 'posher' parts of your town or village. See who can spot the most birds/cars/drain covers (it doesn't matter what it is). If you have younger kids look at the signs in shops - I taught DS his colours and the days of the week by looking at shop windows and the opening times in the shops on his way to nursery when he was little. Nothing is boring at that age!
Teach them to cook like we did last time - that skill is never wasted. Put them in charge of cooking the dinner or making lunch once a week if they enjoy that. Bake a cake or biscuits together and decide on a film or a TV programme you want to sit and watch then enjoy the cake! That's a couple of hours sorted! Have a film afternoon a couple of times a week. The main channels have loads of films or box sets on them so you can do a TV series spread over many days if a film doesn't work for your kids attention span. DS loves West Wing (All4) at the moment. None of us understand a darn thing that's going on most of the time but he loves the pace and drama and comparing the President to Trump! But if those type of things don't work what about DIY or travel - loads on All 4 or BBC/ITV play again.
We're also doing quiz shows like Only Connect, Richard Osman House of Games, The Chase. Just keeps the mind ticking over and you'll be amazed how much your kids actually learn from them and what they know. Same with QI (if you're OK with the swearing). Have a quiz hour when you put a couple of those on every few days.
My DS is an only child. He's currently finishing his class work (young teenager), then he's helping me take down the Christmas decs after lunch. After that he has two hours on the PS4 with his headphones playing with 6 friends on line. They have been doing that since the last lock down started. Every day. They enjoy it and they look forward to it. I don't worry about the time spent on line - I'm on here so I can't talk! It keeps him sane, touches base with friends every day and he enjoys it. I'm happy.
Why not find some pod casts on the BBC (go to BBC.co.uk/sounds) - depending on their ages there are things like News Quiz and You're Dead to Me (which is a history pod cast that looks at a specific thing - like pirates or Boudicca but done in a fun way). There is a kids version but I can't remember it - the presenter of You're Dead to Me does mention it in the opening minutes each time. That's how we stumbled on it. We download these for car journeys - DS loves them. There's a load on there. Plus there are programmes under drama, comedy etc. Have a half an hour 'unwind' session each day or so where you put on a podcast, sit back and just listen. Or do a bit of crafting/art whilst you listen.
Then there's YouTube - DS and DH find things like Michael McIntyre 15 minute funnies or things like riddles - there are amazing numbers of riddle YouTubes out there. You know the sort - a man is in a cave with no windows but he knows he's facing south or whatever. There are even YouTube things on 'add up your score to find out your spiritual animal' which DS used to love when he was a bit younger.
The point is you can see this as a thing to despair about and wish away (whilst not being able to do anything about it) or something that can give you the opportunity to do baking, quizzes, box set blitzes, walks that you normally don't do, drawing/crafting or just lazing on the sofa reading a book or having a nap!
The key is routine. A walk after lunch or a film on a Tuesday and Thursday afternoon, download a quiz show on a Wednesday evening. Apart from grounding you a bit so you're not mind racing all over the place, a routine also helps us as parents. If the kids know it Tuesday film afternoon they have something to look forward to if the on line work is done and you have an aim to get everything done by 2pm or whatever. If you're working from home that's fine. Give them some cake/fruit/biscuits or whatever and stick the film on. Routine, routine, routine and something to look forward to (even if it's a chocolate hob nob at 3pm).