With 3 little ones we always have boxes around our house, mostly diaper boxes. My boys have always had a blast with boxes. They find it pretty entertaining. I had no idea the fun a child can have with a box until my oldest was about 18 months. There was a diaper box waiting to be thrown out and he climbed in it, and had the time of his life. He brought toys in, read books, he even thought it was fun to eat in it. As he got older he got more creative. He would put a couple of boxes together and make it his train. As a side note we are pretty obsessed with trains here at our house so there will probably be an over abundance of train posts.
After my second son was born I was feeling guilty that I wasn't able to play and spend as much time with my first. So one afternoon while my oldest was taking his nap I took a box that he had been playing in that day and turned it into Thomas.
It took about 30 min. Nothing special. I cut off one of the long sides that folds down to make the top of the box so he could get in and out, taped down the small side to be the front of the train, then taped up the back small side to the side I hadn't cut off. Cut half of the longer side off, made a hole for the window and with the scraps I made the funnel. I covered it all in construction paper, cut out some wheels and added the number one. I don't have any pictures of how I made it as I didn't think I would need any. Just sort of made it on a whim.
He LOVED it! I think that box was around our house for a few months before I finally threw it out.
Here are some pictures of "Thomas" Nothing amazing, but for kids it isn't about that, they don't care if it is perfect, which is a good thing because none of my creations are ever perfect, or come close to it. But my kids love them. If you look hard you can see I ran out of blue construction paper so the front isn't even all the way covered.
And this was the start of our box creations.