Here are a few examples of some team games. The teams can be small (1-3 children) or big (15-20 children). We start with some games for small children.
a) One team places a number of stones in front of itself. The other team has to:
1st game - place as many stones, or
2nd game count and say how many they are, or
3rd game - add as many stones as necessary to make 14 stones, say, or
4th game - take away some stones to leave 3, etc.
As the game progresses you could get them to learn the number names, too.
b) One team throws two dice (with dots or with numerals on them) and picks up, from the collection of stones in the centre, as many stones as the sum (or difference, or product) of the numbers shown on the dice.
The other team does the same. After two turns whoever has more stones wins.
Again, they could get used to the language like 'six plus two equals eight'.
c) With stones, twigs, dice, cards or beads you can design games to teach 'place value'. With 10 stones (for base 10) being equivalent to one card or one bead, exchanges can be made and records can be kept. Once they are able to grasp the notion of tens and ones in concrete forms, they can be exposed to games using numerals.
For example, you could take two sets of ten cards each, numbered from zero to nine, to be used by two groups. The children shuffle the cards and place them face down on the table. Then they take turns to select one card at a time and place it on the board, in the column marked 'units' or 'tens'. The aim is to make the largest possible number, and once a card is placed, it cannot be removed. As they play, they loudly say the number they are making. For example, if the first group turns over 3, and places it under 'tens', they should say 'thirty', and so on.