We do a few different things depending on whether I am home that afternoon (if child's activity is nearby I can just drop and come home), or whether I need to wait for DC at the activity so I need to do something quickly as we get home at 5.45 or so and all are hungry.
On a Sunday I usually cook enough for 2 evening meals - e.g. spag bol, a roast, lasagne, casserole, curry, roast, chunky soup or whatever and we have leftovers the following night that can be reheated quickly once we get home from the activity with hungry children. So that's Sunday and Monday sorted.
I cook 'properly' x 2 again of a Thurs as I have more time that afternoon, albeit we all eat it early before the activity, and then we have the leftovers reheated on the Fri when we all get back at 5.45.
So that just leaves Tues and Wed to cover. (Sat H is home and no evening activities so all is good).
On nights where we get back late and I still need to make a meal from scratch, I do something quick - e.g. salmon, broccoli, peas and noodles. Takes 15 mins once the oven has warmed up so it's quite fast. Or baked other type of fish, chopped up home made 'chips' (i.e. just normal potatoes in small slices) plus veg is quite quick-ish.
I also have an emergency quick meal in mind at all times in case the toddler doesn't nap and is clingy and we are all tired and hungry and can't wait long. One go to meal is gnocchi and a jar of sauce plus grated cheese (literally 5 mins from start of heating water to serving on the plate). Not ideal maybe for some people with processed sauce and gnocchi but it works, is warm and filling and everyone likes it. The gnocci is long life so keeps in the fridge for several weeks waiting for a meal 'emergency', and it's cheap, quick and filling. I tend to add extra veg into the jar of sauce e.g. grated carrots, mushrooms, courgettes etc.
For the after school activities which are physical ones and require feeding the child before the activity, I do a early light tea for the exercising child (ie 1/2 to 2/3 of the portion that they'd usually eat so they aren't too full when exercising), then they eat part 2 of their tea portion plus some yogurt and fruit/pudding when they get home at 8pm. Also, I sometimes do a small serve of beans on toast or egg on toast if DC needs feeding pre activity if the main meal isn't ready yet.