At dd's first birthday, we mainly just hung out - the kids were young and couldn't do too much interactively - organized games wouldn't have gone over very well.
This year for dd's second b-day (which is in 3 weeks), I'm having a Blue's Clues theme. I found a whole bunch of free printables online (just google "Blu'es Clues printables"), and I'm going to set up separate little play areas to cater to the different ages of the lo's (there will be another 2 year old, an 18 month old, a 4 year old, and an 8 year old attending).
So one area will be like arts and crafts, one will be playdough, one will be decorating Blue's Clues cupcakes, one will be fingerpainting, etc. I'm trying to have something for each attendees interests and age appropriateness.
HTH,
Jenn.