I want to pack some sandwiches for an upcoming picnic with my 6yo twins, but want it to have some green veggies. Could anybody suggest some ideas please?

How about egg spinach grilled cheese sandwiches? They are easy to make and contain ingredients that you probably have in your fridge already: egg, cheese, spinach, butter and bread. After frying the egg, assemble the sandwich and butter the top and base of the sandwich. Using the same pan you used to fry the egg, grilled the sandwich till golden brown. If you have a panini press, you can use that too. The result will be warm, melty sandwich oozing with eggy and cheesy goodness. The spinach add a healthy touch!