A craft table is always great - my 4 year old's party in September was a Teddy Bears Picnic, so we made bear masks (paper plates with the eyes already cut out) and did 'beary' colouring and collages (lots of bear shaped and coloured bits and pieces, a big tub of crayons and some Tesco pritt stick (10 sticks for a pound on the end of aisle displays)).
If you google colouring images, you'll get loads of printable pages for whatever theme you want.
Eye Spy was a good game to keep them quiet for 10 minutes while the tables were set out, or for the last few minutes of the party - we tied it into the Brown Bear Brown Bear story and had put pictures/toys around the hall that fitted into the story. You could do the same with stories such as The Very Hungry Caterpillar or There Was An Old Lady (which can also be sung of course).
Simple games like follow the leader and the hokey cokey are good for this age group.
We also played a variation on corners/islands - which is basically to choose 4 'things' (coloured paper islands, or toys/signs/people etc around the room), play music and get the kids dancing, and when it stops everyone has to go to one of the 'things'. An adult (who hasn't been looking) then calls out one 'thing', and everyone there is out (give them a consolation sweet, or medals are popular). The last one in is the winner.
DFW Nerd no. 884 - Proud to be dealing with have dealt with my debts