I had this problem during lockdown when mine were toddlers, the days seemed so long. I found it helpful to block out the day and with each 'block' we'd change room and do a different activity, or go outside, tire them out and and then come in and do something cosier/more relaxing. Some ideas:
-Daytime bath: let them play in the water for ages with bath toys, or even pots and pans, sieves etc to play with the water. I used to do this especially after being outside if the weather was cold.
-Build a fort out of cushions etc, then sit inside and read stories. If you have a yoto or toniebox even better as they might sit in for a while longer themselves and listen while they draw, colour etc
-Jigsaw hunt: hide the pieces of a jigsaw all around a room, or even in a few rooms. Then they hunt to find all the pieces and put the jigsaw together... takes up a fair bit of time. Mine liked to hide the pieces for me as well, and would take ages to find hiding places. If they're too young for the jigsaws to have many pieces you could even hide a few different ones at a time.
-Cleaning/cooking: Sometimes I'd just get on with housework and give them a 'job' to do like finding all the socks in the laundry basket, or give them a spray bottle of water and a cloth and let them clean the surfaces or the windows. Mine also loved 'helping' when I'd make lunch, dinner etc, I'd just give them those child-friendly knives and get them to chop up bananas or whatever
-Small world play: build houses/towers for little toys out of blocks or duplo. I sometimes showed them a picture of a particular structure/shape and asked if they could make one like that as it kept them focused for longer if they had a challenge.
-Playdoh/ crafts: again, I found they'd play longer if we had some pictures of shapes they could try to make, then I'd guess what they'd made. We had a pack of animal playing cards so sometimes they'd pick a card and try to make that animal. Could do the same for drawing or painting
-Dance party: turn on music and get them to play musical bumps or musical statues when the music stops, even if there's only 2 of them, it tires them out (and then you can watch a film or something afterwards)
-Role play: I'd read them a story about a restaurant/vet/doctors/shop or something to get interested and then we'd set up our own one and play for a while, taking turns at the different parts ie shopkeeper, customer, robber. Setting it up killed some time and so did putting it away. Very handy if you have some dress up, even a few bits, and accessories like a till or a doctor's kit to bandage up the dolls and teddies.
-Toy rotation: sometimes I'd set up/hide a few toys in each room, so we'd go exploring to see what toys we could find in one room, play with them for a while, then after 20 mins or whatever, move to another toy in a different room for change of scene. For this I'd really just follow with a cup of tea and feign surprise 'oh how did that get in here? Let's see what else we can find' etc
Not sure if you have a garden but I found certain toys a lifesaver as they'd go on them repetitively with no input needed from me - the 'step 2 up & down roller coaster', could be used inside if you've no garden. Sandpit was (still is) very popular here and they'd spend ages in it by themselves, again you could have this indoors. Same with swings.
Hope some of this is helpful! If I was feeling cabin feverish I tended to just bring them out for a walk as I could never face more than 3-4 hours at home! And then I wouldn't feel guilty about watching a bit of tv with them when we came back