L.B.
My first thought was take a valium and have a glass of wine - but, oops, you meant what to do *with* the children.
Get lots of indoor activity items -arts and crafty things - set up a huge table and have directed play time. Play tent in the living room, maybe a small limbo game.
They will need activities that are physical in nature, but you can control those activities so you don't have a mini Lord of the Flies scenario on your hands.
I did a quick Google search for "Party games for 4 year olds" and found the following. There were a ton more sites. Most games used simple household items.
http://www.funburst.com/index.cfm
http://www.best-preschool-games.com/index.html
http://www.todaysparent.com/craftsactivities/article.jsp?...
http://www.ehow.com/list_###-###-####_birthday-party-game...
Have Fun !!!