When my son was three and four, he was addicted to trains. He drove me crazy since every toy, DVD and book centred only on this topic (he has had several obsessions since then which have additionally drove me to distraction!).
If you know a little one with a similar interest, we have quite the backyard here in Calgary for watching and learning about trains. Here are some ideas…
Visit the Grain Academy Museum (free) at the BMO Centre. It includes quite a bit of railroad history too. This is a real fav for those who enjoy model railways too.
For those who like locomotives, there is no avoiding Heritage Park. My son was only into diesel engines but he did like going on the train nonetheless! And remember that in the Christmas season, they have model trains set up in one of the historical shops as well. My son enjoyed the Glenbow museum (for short periods at a time) as well. (This page provides some interesting links for older children to review historical photographs, routes and artifacts.)
Head out to Supertrain 2011 in April. Lots of model railways set up for viewing…I could not believe how much time was invested just preparing the landscapes for some of these! My son’s birthday coincides with this annual event in April so we took the kids here before heading home for cake.