Boys love trains. There is no reason that your toddler's room has to be all Thomas the Train bright and cartoony. Below is some inspiration on how to add a little sophistication to your choo choo room.
Vintage antique train hook and magnetic board - this one is on etsy at Shugabee Lane
Hand-tufted train rug - currently available at Overstock.com
Ride on Choo Choo - by Pegperego - Of course it's been a fantasy since Silver Spoons to have an adult size version of one of these, but this one looks like it would be pretty fun for your little one too.
Customized Transit poster - pick your cities and your colors at Transit Design's Etsy Shop
Turn a vintage suitcase into a side table - learn how to DIY at Lark and Lola
Train Bedding set from Land of Nod
Choo Choo Train wall art - handmade prints on wood wall panels from Skartshop
Handmade wood pull train - a great toy when they are young and a great decoration piece as they get older. This one is from Woman Woodworker on Etsy
Other ideas to add a little sophistication: Incorporate some navy ticking fabric or wallpaper emulating the pattern found on a train engineer's cap. Add a vintage club chair reminiscent of the golden age of train travel.