We did the one below with what we happened to have in the kitchen, namely:
1 clove of garlic
half a yellow pepper
three leaves of swiss chard (both the green and the white bits)
2 table spoons of olive oil
750 ml of water (no need to bother with stock - it will be less flavoursome but more healthy)
salt and pepper
1 bay leave
you can add a couple of potatoes, or a courgette, or green beans, a bit of parsley... you name it.
Heat the oil on a (deep) pan over medium to high heat. Add all the vegetables cut into cubes (not too small). Add also the bay leave and the salt. When it starts getting golden add the water (we added it cold but if you are in a hurry just add hot water from the kettle) When you see the first bubbles reduce the heat to low, wait for 10 minutes and then take the bay leave out and blend the soup either with a hand blender (easier) or in a normal blender. Add more salt if needed and some pepper. You can serve this soup with a bit of cream, or with croutons, or with some boiled egg cut into small cubes on top.
The kids can and did help with all of this but they need supervision as the water gets very hot. They like experimenting with vegetable combinations that would work well. Carrots, onions, courgettes and leeks are our current winner.