My three year old has quite an extended family and the kids are all different age groups.  We had a Thomas the Tank Engine party where everyone who came took their picture as Engineer of our "Thomas".  We used boxes to decorate as the train and cars and after the kids took their pictures with a Polaroid camera, they got to keep their picture. The older kids decorated cupcakes and the for the younger kids - I taped many pictures together that I printed off with different trains on them and put them on one large wall.  The kids were then given colored chalk to "color on the wall".  The colored chalk wipes off easily. I also filled a large balloon with candy and toys instead of a piñata and let the birthday boy bust the balloon.  Of course we immediately picked up the balloon pieces and the kids had a wonderful time picking up candy and toys for their bags.  For the younger kids, we set up a large bowl full of water and I bought some small plastic fish and put numbers on them. The numbers did not mean anything, but the small youngsters chose a fish and traded it for a prize. Just like at a carnival. This was a big hit and even some of the older kids wanted to try it - so we let them!  The cake was simple with a forest scene and I added railroad tracks with colored icing and then added my son's wooden Thomas trains. Every child went home with a Thomas goodie bag and they also took home a balloon of their choice.