Wikipedia, the free internet encyclopedia, says:
"Connect Four (also known as Plot Four, Four In A Row, and Four In A Line) is a
two-player board game in which the players take turns in dropping discs into a vertical grid
with the objective of getting four of one's own discs in a line.
The game was published by Milton Bradley in 1974; a non-proprietary version is known as
'The Captain's Mistress'."
Play Connect Four with your kids. It helps them 'see' and 'create' diagonals and doesn't have the frequent draws (i.e. no winner) that Tic-Tac-Toe can have.
However, if Connect Four is too frustrating for your kids have them play Tic-Tac-Toe until they discover a strategy and can move back to Connect Four.
Connect Four Yahoo Search: On December 20, 2006 I got 25,800,000 hits using this search.
Connect Four Google Search: On December 31, 2006 I got 17,500,000 hits using this search, so you can find many versions to play or buy.