So my daughter just turned 6 and we had a conversation a few weeks ago:
Her: Daddy, do you know why I don't run my Thomas Train anymore?
Me: No, why?
Her: I don't like Thomas anymore...
After thinking about it for a few minutes (and since I completed a few custom box cars - Cubs Championship Car and Wisconsin Badger Car), I asked her if she would like to do a project over the summer to get some passenger cars an paint them together. I already had an older Polar Express Engine plus I had an extra shell I had intended to use for my Hanukkah Train, but I ended up not using it in lieu of another engine. I offered those to her as well. So she quickly said yes, she would love to do that, and she wanted to make a Rainbow Train we would call The Sarah Express.
So things moved faster than doing it over the summer...
I found some older Milwaukee Road Passenger Cars and got 6 of them. After prepping them, and the engine, I helped her spray them with primer and then the colors. On the engine, we added Navy Blue to the boiler, tender, and passenger car roofs. Then each passenger car was painted a color of the rainbow. We put everything back together today. There are a few things to touch up, lighting to fix, and they need decals, but she loves the new train. Here are some pictures of our endeavor and a video of it running: