Here is a birthday invitation i did for a client that had commissioned me to work on several projects for them:
1- their wedding invitations, 2- their wedding program, 3- their wedding photography, 4- their 1st family pictures, 5- their little boy's first birthday party pictures and finally, when their baby boy turned two, they asked me to create some invitations for his birthday party. the suite included a design that replicated a train ticket, the back (which i wont show here due to privacy purposes) had a picture of their son that all invitees, regardless if they could come, could save as a keepsake. and the party bags were craft bags with a folded top sealed with my tag.
Here are the samples from that set:
I am a Brooklyn based graphic designer, and would love to help you create a train, railroad theme for your little ones party. reach out to me on my site - http://bit.ly/1k21V3C