Connect Four
Four Square
Fore! (as in golf)
Four Seasons
Four corners of the earth
ETA: Sure! I would suggest picking a theme that has to do with the number four, since you have that common link. I apologize if you know some of the stuff I am going to explain, I am going to assume that you may not have gotten all of the language/cultural references.
Connect Four is a very popual board game: http://www.amazon.com/Hasbro-4430-Connect-Four/dp/B00000IWI1
Pretty much anyone who grew up in the 70's-80's in the US played it when they were young. The pieces are red and black checkers in a bright yellow grid, so you could do a lot with decorations. You could set up a Connect Four tournament- it is a simple enough game that 4 and 40 year olds can both play and enjoy it! You could do cupcakes with yellow frosting and either a red or black licorice wheel on top, things like that.
Four Square is also a childhood game, played using the red bouncy playground balls and a "court" that is a large square drawn on the ground and divided into 4 squares. Again, you could have a tournament, those this would have to be outside or in a bid area like a gym. Decorations could be red, maybe throw in some other old-school playground things like jumpropes.
Fore! is something that golfers would recognize, it is a golf term that basically equates to "heads up!" So you could do a whole golf theme, I love the mini golf suggestion.
Four Seasons- you could do summer, fall, spring, winter activities. For example, decorate holiday cookies, carve pumpkins, decorate/hide Easter Eggs (or other cultural activity for spring), have a water balloon fight or smores and sparklers.
Four corners of the earth- pick four different countries that are spread far apart and choose a childhood game from each one and a food/beverage specialty from each one. Games for the kids (though fun for adults, too), food tasting for the adults.
I hope that helps!