I think you need to give yourself a break thinking you need to "cook properly" every night.
Find some shortcuts too.
I was a single mum too and it's a grind.
The occasional "freezer to oven" meal won't kill them or you.
If you're making something that can be frozen and eaten as a leftover always make at least twice as much as you need (dependent on freezer space of course) you'll soon build up a stock of "home made ready meals"
Use convenience foods that are actually good for them - Tinned tomatoes, ready to eat or quick cook/microwaveable grains, Tinned fish, frozen fruit and veg...
Meal plan - yes it's a chore at the time but saves you time and food waste later
Choose simple options -
Eg fresh pasta with cream cheese stirred in as a sauce, Chuck some cherry tomatoes, Tinned sweet corn or whatever on for the veg bit. Adding the veg cold actually cools the dish down just enough that kids can eat straight away in my experience
Cous cous was used a LOT in my house when dd was growing up as it's so quick and easy to do! I'd make it in the bowl I'm serving the finished dish in to save on washing up too!
"Stuff on toast" - perfectly adequate for little ones and you can supplement your own version with preferred added extras
Eggs with everything - healthy, filling and cheap! You can even do them in the oven on an "I can't be arsed day" just crack into an oiled ramekin, if you like pop some grated cheese on top, bake for around 20 mins which is also around how long most oven chips/wedges take! You can even cook beans or indeed any Tinned veg in the oven in a ramekin or similar too, but put some kind of lid on or they can dry out
Soup is an easy thing to batch cook and freeze and can easily be a meal in itself especially if served with a roll or sandwich
Nothing wrong with the occasional "picnic tea" either - picnic/buffet items like quiche. Sausage rolls, scotch eggs (quorn do lovely mini ones), falafel, cocktail sausages, mini or slices of pork pie, crudités and dips, cherry toms, pickles, bread sticks, crackers, cheese portions, Deli slices, olives, sundried tomatoes... providing a good balance of nutrients absolutely fine and one of my dds favourites growing up
jackets ate fine my favourite filling is cottage cheese and sweet corn
Nothing wrong with instant mash either goes great with casserole type dishes