when I've had 4 hours sleep thanks to 2 year old
Is this a regular thing, OP? If so, are you taking steps to deal with the sleep problem? You need to be well-slept to cope with work and if you're constantly feeling faint from lack of sleep, you won't be able to continue.
I know it's the last thing you feel like, and I know lots of people think a day in front of tv is fine, but it won't help the poor sleeping at all - they need to be out running that energy off. Also, you say they lose interest quickly, so it's not really solving your problem. They're hardly going to sleep better if they've been lolling around staring at a screen for hours on end, so while a bit of tv won't do any harm, it's not helping your situation longer-term.
If you need to sit down, do it while they're playing nicely for that first hour and then (before it descends into squabbling chaos) grab their coats and get them out - reins on 2 year old until he learns to walk nicely.
When you say your 2 year old is a bolter, do you mean he doesn't listen to you, or does he definitely hear you but ignore? That needs working on as well - once you have the sleep sorted.
I certainly don't think we should be entertaining children all day long; they need to learn to play by themselves, so don't feel you need to be constantly providing fun - give them things like water (or the bubbles game previous poster suggested), play dough, and so on - and don't allow your 2 year old to spoil things for your older dc. Each time he hits/grabs, lift him away and let your 4 year old see that you're in charge. At 2, your toddler is old enough to be told No and your older dc shouldn't have her/his play constantly spoiled.
It's no fun feeling so exhausted - so take care of yourself. Eat properly, get out for some fresh air, and tackle the sleep problem, if you aren't already. Good luck 