My son recently celebrated his 3rd birthday. We are lucky that here in Scottsdale, we have a train park that has a train ride.  We let the train park host the first hour of the the party, and that went well. They played a couple of games easy enough for 3 year olds...red light green light, popcorn with a parachute and balls, and tug-o-war. After the games, we served cake and ice cream. The cake was great.  We bought an N scale train set, and had it put on a half sheet cake at a local grocery store. If you have a toy" you want on the top of the cake most stores are willing to do it as long as the toy is in it's original packaging unopened. It was much cheaper than a shape cake from the local specialty bakery and my son will have the set to play with for the next couple of years. After the hosted party was over we served pizza and set up wooden train tracks for the kids to play with in one of the park ramadas.  We  shopped on Craig's list for a week or two before the party and got several sets of tracks and used trains for less than a bouncer would have cost us.  It worked wonderfully!!! The kids were totally mesmerized with the tracks and trains and some kids played for a couple of hours.  The parents were able to sit around and visit and the kids were fixated on the trains...boys and girls alike. Since it was the beginning of the school year for preschool most of us parents didn't know each other. This gave us the opportunity to visit and watch the kids interact. For party favors we bought crayons and train coloring books ring pops from Costco and some cheap plastic train whistles.  The kids loved it and we have heard nothing but praises from our guests."