For children, ice-cream sodas can simply be a matter of placing two scoops of ice cream into a sundae glass (or a tumbler will do). Pour over 75ml of cordial and adding a bottle of soda - which will give it a beautiful frothy head.
Instead of soda and cordial you could pour cola or authentic lemonade for the same effect; what it must have is some fizz. You'll need to give everyone a straw and a long spoon.
For a more special ice-cream soda, make up some lemon syrup as for Home-made Lemonade (see below) and assemble as above.
Sundae glasses or tumblers