Cut the oranges in half and juice them. Pour the juice into a jug. If your children don't "love" seeds and filaments in their freshly squeezed juice, you can strain it.
Fill each glass ¾ with orange juice and then add a little soda water: it's basically like very fizzy water (which you can use in alternative, if you don't have any soda water on hand), but creates that bubbly effect and that atmosphere (a bit) like being in a "bar" which no child - not even the most recalcitrant - can resist. If you have some, you can also add one or two ice cubes in each glass.
Grownups can naturally, if they wish, also replace the soda water with some "bubbly".