Iceland do a 'Sunday dinner' for under £10, I know you said you sometimes have a roast but doing everything from frozen is quicker and easier.
You can also roast in a slow cooker, just put a joint or a chicken in before work and come home to a cooked meat - serve with veg or salad and bread.
Meatballs are easy to make and to add ingredients, so Italian meatballs in pasta with cheese or Chinese style with a broth.
My carer (not a cook but I was ill) made some under instruction from me.
Minced pork
salt and pepper
one red pepper finely sliced and then cut into squares
1/2 each of frozen garlic and ginger 'cubes'
a teaspoon of chilli powder, cumin and paprika
Make into balls the size of walnuts
For the broth, 2 spring onions chopped, a veg stock cube, the left over garlic - add boiling water and stir until the stock cube is dissolved.
Add the meatballs tot he broth and cook for 10 mins - they will float when cooked.
Even easier if you don't like spice
mix of beef mince and pork sausage meat, add salt and pepper divide into balls.
1 pack passatta
optional cheese
Place in an ovenproof dish and pour over a packet of passatta.
If you are using cheese add it now - mozzarella torn up or grated cheddar put in the oven for 20-30 mins and serve with pasta.
The easiest pasta 'dish' ever
dried pasta of any shape, 1 packet of cream cheese.
Put in the pasta in a pan pan to cook. Once it is done turn off the pan but do not drain.
In a frying pan add some cream cheese - about a desert spoon per serving, ass a dessert spoon of the pasta cooking water and stir on the heat. You will end up with a creamy sauce, toss the pasta n it and serve.
Now the magic of this is that once you have done it once you can add to it, salt and pepper are obvious but you can fry a couple of mushrooms in the pan before add in the cheese. Or onion and herbs, or streaky bacon / lardons, or leeks.
You can also add things after cooking, lemon juice, olives, fresh herbs.
Depending on how old your children are they can either help or make this themselves.