I'm sorry you are feeling stressed and down.
Ignore any judgey comments - your children are very young and at that age, kids are bloody hard work! I only have one who is now 11 and an absolute dream, but I found the under 4 years stage so bloody hard!
Like yours, his attention span wasn't great and he needed entertaining.
Lots of good suggestions on here already, so apologies if I repeat any.
Could you take them swimming? Most council pools will be open except for the main holiday days. I know that might seem like hard work and it does depend if they like water, but it's generally fairly cheap and will tire them out. I used to take ds in the morning and then he would be calmer in the afternoon.
Definitely embrace soft play - I know it's grim for adults but kids like it, you can get a brew and it's mess and noise somewhere that isn't your house.
Some libraries also have a few toys/colouring bits so definitely see if they are open - again, we were regulars at ours. DS loved the books/toys/colouring and it was out of the house.
If you can afford to, take them to a supermarket cafe for lunch/tea - my ds still loves tesco cafe 😂😂 kids meals are usually fairly cheap and you can either eat or just grab a drink/cake. Again, keeps them entertained/fed/mess not at your house (see the theme emerging here 😂)
Basically, I used to aim to do something out of the house every day - cheap if possible or free - we have bridle ways near us - if you have paths locally, use those, let both walk but take buggy for when youngest gets tired.
Good luck!