That's a pretty wide age range, but they are all still pretty "little" kids so a lot of the old standards I think would still be fun for them all:
-Musical chairs (an older child/adult could help the little ones so they can also join in)
-Pass the Parcel (wrap a small gift in a many layers of wrapping paper and pass the gift around to music. When the music stops, whoever has the gift gets to unwrap one layer. You can manipulate the game so each child has a chance to unwrap a layer. Whoever unwraps the last layer gets to keep the gift as a prize).
-Pinatas are always fun for any age! A tip I've found useful is to draw a circle around the pinata that the kids cannot enter, only the one with the stick. This helps to create a safe distance so no one gets wacked! Another tip is to line up by size and let the littlest hit first (usually without a bandana) and as the kids get older/bigger they are blindfolded.
-Hide the Candles - you can print out and cut out about a dozen or so pictures of birthday candles. Then let the birthday boy/girl hide the paper candles all around a room while the others hide their eyes & then all the guests get to hunt for all the candles.
-Coloring Table - a good time passer if guests arrive early or for a time filler during the party, is to have a coloring table with all sorts of photo copied pictures of birthday related pictures and a bunch of crayons/markers/colored pencils whichever works best for the age group.
Hope some of these ideas help :) Have fun at the party!