Concentration, also known as Memory, is a great family card game. It's easy to customize the rules to make the game easier or more difficult, and younger players tend to be able to compete with older players because they generally excel at memory-based games.
This is a game for 1 to 6 players. The only equipment necessary is a standard 52-card deck. The object of the game is to collect the most pairs of cards.
Shuffle the cards and lay them on the table, face down, in a pattern (e.g. 4 cards x 13 cards). The youngest player goes first and plays then proceeds clockwise. On each turn, a player turns over two cards (one at a time) and keeps them if they match numbers. If they successfully match a pair of numbers, that player also gets to take another turn.
When a player turns over two cards that do not match numbers, those cards are turned face down again and it becomes the next player’s turn.
To make the game easier, cards can be removed in sets of 4 (e.g. all of the 2s and 3s).
To make the game more difficult, require players to match both numbers and colors, as opposed to just numbers (e.g. The King of hearts would match the King of diamonds, but neither of those cards would match the King of clubs).
In a one-player situation, time yourself to see how fast you can find all of the matching pairs. Compete with yourself by trying to get a faster time in a second game.
With two to four players, keep each pair you find. At the end of the game, each pair scores one point. When all the pairs have been found, the player with the most points wins.