Now that we know we are having a boy, I am thinking boy themes a lot! Trains are always a great one. Don't forget about older, but still fresh!, Frosting for a train theme here (link)
Setup a fun table using a sky backdrop and containers filled with snacks to make a train! To create different heights, look around the house for boxes and other household items you can cover with green wrapping paper. Source
If you have a train set, set that up and use it to display your cupcakes! Source
Set up some great fun with large boxes (ask your local businesses if you can gave them before they toss them!) creating a train! Have the kids sit in for an outdoor movie or singing songs, etc. Source
For your favors, create these candy trains! Source