This idea is to show children that addition can be done in any order but subtraction cannot.
I showed year 2 children addition facts to 10 and 20 can be done in any order by placing 10 (and 20) pegs on a coathanger, putting 2 pegs at one end and 8 at the other. Children count the total and can visually see there are 10. Then by repeating 2 at one end and 8 at the other, turn the hanger around to show that addition can be done in any order. This works with up to 20 pegs.
You can also show how subtraction cannot be done in any order by the same process children can visually see that 8 pegs cannot be taken away from 2 and leave the same answer as 2 take away 8.