Once upon a time we were keeping a couple of the great grand kids and one asked me if we had a train.   In about the time for a small child to take a nap I went to the shop to see what I had that looked like a train.   A few 2x4s, misc wood blocks, dowels, screw eyes, and screw hooks, this is what I came up with.   The "train" was a smash, all great grand kids that come to our house get it out and play with it.   It is one of the first out of the toy box.   BTW- I didn't paint any of these, hence I didn't have to worry about toxic paint.

On another ocassion, a great grand daughter (about 18 mo.) was there when I came home from picking up a couple of 9mm magazines.   She pounced on one and carried it around for the rest of her stay shaking it because it rattled.   After she left, I replaced the magazine with a wooden block, she still gets it out of the toy box and goes around rattling it each time she visits.   Pic.

A locomotive?   You can just see the screw eye as the rear coupler.   I rounded off the corners with a disk sander, the cab is a smaller piece of wood, the smoke stack a dowel, and a small dowel for the whistle (it had to have one according to Ian).

The locomotive again.   I used a marker to draw the wheels and the green lights on the front.

I was thinking about passenger cars when I did this.   You can see the hook front coupler.

A tank car.   Two dowels of different sizes and a flat base produced a tank car.   The base had to be big enough to draw the wheels and hold the couplers.   There are two wallboard screws holding the "tank" on.

The Caboose.   A large and small block of wood glued together.   You can see the marker work for the tail light above the rear coupler.

Heres Ian playing with the "train".   For about an hours work, the kids thought it was great, each one of them play with it every time they visit.

The large hooks and eyes make it easy for the kids to couple and uncouple, the cars in any sequence.

I was surprised that Ivy thought a plastic box with a wooden block inside was a great toy, she carried it around for quite a while shaking it.