A Grinch Who Stole Christmas Party is a unique and fun party idea, great for the family friendly party!
For invitations you could do very unique wording, such as: "A Who invites you to attend an evening of celebrations and singing." Have your invitation in the shape of a snowflake as the Who's live on a snowflake. Another suggestion would be the shape of a heart.
For decorations hang snowflakes and tree ornaments with fishing wire from the ceiling. Decorate a sleigh for the front yard. If possible have a fake dog with antlers on it pulling the sleigh.
Have Santa hats and reindeer antler hats as party favors for all.
Your food, you could have heart shapeed and tree shaped cookies.
In the background have the Grinch who Stole Christmas playing on the tv, with the volume turned down. Play festive Christmas music on your Ipod for all to hear.