An important part of Key Stage 1 maths is fluency with addition and subtraction of single digit numbers.
A significant step towards this is to play around with all the possible combinations of numbers which add up to 10, so called number bonds. Possibilities are:
0+10, 1+9, 2+8, 3+7, 4+6, 5+5, 6+4, 7+3, 8+2, 9+1, 10+0
They are as important as times tables. When confronted with difficult 3-digit addition and subtraction sums in KS2, it really helps to be able to instantly recall number bonds.
There are lots of fun ways for children to explore them, not least games. This one from mathplayground.com is one of my favourites; number_bonds_10.
The player has to shoot a numbered ball at a line of advancing numbered balls to make the correct number bond to 10. Get it right and the balls disappear. The aim of the game is to make all the advancing balls disappear before they reach the end tube. Its not as easy as it sounds! Keeping track of where all the numbered balls are uses quite a lot of brain power, which means you really have to know those number bonds..