I found this paper doll railroad train from an Etsy seller, which I printed out as postcards. The boys were pretty excited to check the mail everyday to see if they got any new puzzle pieces. On one day they received eight cards, that was a fun afternoon.
We have been putting them together to drive our trains on. I asked people to add a note or draw a picture and we absolutely love the personal touches that were added. A huge Thank you to all who mailed theirs back!