Beach games:

Keep Your Bottle
This game is particularly good at family parties or with mixed age groups, and is definitely a warm weather, outdoor game! A great game for a large beach party.

The Splash Game
Not for the faint-hearted, this game is best played out of doors when clothes don't really matter! It works with mixed family age-groups if everyone who takes part is a good sport, and will cause much hilarity..

Ping Pong Ball Race
Dig a series of sloping channels wide enough (and smooth enough) to take a ping pong ball. Make them equal length, or have slightly longer channels for older children and adults. Place a ping pong ball at one end and then race each other blowing the ball down the channel to the finish line.

Beach Mini Golf
Make your own mini golf course in the sand. Players take turns with a plastic golf club and ball - or whatever you have to hand that you can improvise with.

Frisbee
Get the Frisbee out and challenge the family to a game.
Set up some targets in the sand and see who can throw the Frisbee nearest to them.
Set up some "bottles" (plastic, please!) in the sand, and see who can knock them over.
Play Frisbee golf. Make your own devious course in the sand and take it in turns to complete a "hole", which might be a circle marked out in the sand. Perhaps you will have to go around the picnic basket to get there?
Just throwing a Frisbee back and forth between players can be enough to keep children entertained for a good long while

Beach Volleyball
Some beaches have a proper volleyball court but it is often monopolised by older children and young adults. If there is space on the beach you can always set up your own version, improvising with windbreaks, picnic baskets or a portable badminton net. Make up your own rules, too.

French cricket
French Cricket is a very popular game with older children and teenagers, but it is fun in a family gathering too. You need at least 6 players for a good game, and a fairly large space to play.

Bowls (boules, petanque)
It is definitely worth investing in a set of plastic bowls for a day at the beach, especially if you are going with a mixed age-group - it seems to be a game that grandparents particularly enjoy! Or improvise your own: you will need 4 pairs of matching balls in an appropriate size for your children, as well as a small ball to act as the target.

source: http://www.activityvillage.co.uk/beach_games_and_activities.htm