At this age too much organisation doen't work that well. They don't have the concentration to play too many games.
At ds's 3rd birthday party (9 children in total ages 2.5 - 4 yrs old) I did the following:
1 I provided lots of toys/ride ones etc
2 I put a table of playdoh and various cutters out on a small table with a few chairs.
3 I had another table with a few small chairs which had some templates for a paper crown (easy to cut out in advance) and lots of shiny stickers, glue and stuff to decorate them.
The children arrived and they played with the toys, playdoh and some of them made crowns (helped by any nearby adult)
They all happily played with whatever they wanted to.
When it looked like this entertainment was beginning to wear off (about 40-50mins)we had a couple of games (pass the parcel, pin the tail on the donkey and musical statues) This took about 20 mins.
Then they sat down to tea, had the cake and when that was over they all played a bit more with ballons and a bubble making machine.
That was it - it all lasted about 1.5 - 2 hrs max in total I think. I found that was plenty at that age.
When I had a party for ds