For DS birthday up to age 3 we just got lots of toys out of the toy library, sand play water play, tunnels, huge blocks etc. Have balloons and party bags for the older kids and if you have a few in the older age group (10-14) maybe hire a gamesystem for them from the video store if you are worried about them getting bored.

I think the first game we did was pass the parcel but they didn't really get it and it led to more tears then smiles.

Have fun planning