Most of those old toy trains still have a lot of life in them, but it will help to clean them up and oil them.

Here's what I do to restore old trains:

First, clean, lube and oil the engine. You should be able to remove the plastic or cast-metal shell from the motor by removing a few screws. Don't remove any screws that aren't attaching the shell to the motor. If the shell or any of the cars are dirty, use some dish detergent in water and a soft cloth to clean them.

Lionel used whale oil (really!) on their trains until some time around 1960. By now, it has broken down into gunk that slows things down rather than making the wheels and gears turn more smoothly. So you should use something like isopropyl alcohol or carburetor cleaner to clean the gunk off anyplace where you see metal turning against metal. Don't let the cleaner get close to painted surfaces on the shell or it might clean off the paint.

If the original owners had a family cat, there's probably lots of cat hair inside the locomotive, too. Clean it all out.

After you clean the locomotive, use light machine oil (sewing machine oil works well) to oil all the bearings, and some kind of grease (I use graphite grease) on the gears. Now move the driving wheels by hand to spread the grease around the gear drive. They should turn smoothly and quietly.

There's probably a wire running from the electrical pickup that runs along the center track to the motor. If the wire has broken loose from the contactor, you'll have to solder it back into place. It's usually obvious where it should go.

Now look at the wheels on the engine and all the cars. Clean off the old gunk, and put a small drop of oil on each bearing, where the shaft holding the wheels turns in a socket. Don't oil wheels made after about 1970, because they use a delrin (like teflon) bearing that doesn't need any oil.

Finally, look at each wheel on both the engine and the cars. There's almost always a black ring of old caked oil and dirt around the surface where the wheel ran on top of the track. Scrape off the crud with a knife or some other sharp tool like a small chisel. This will reduce friction and improve the electrical contact between the wheels and the track.

You can get an inexpensive small secondhand transformer that will be enough to power your train at a Lionel dealer or a swap meet, usually for $10 or less. The serious collectors and operators prefer the bigger transformers, so the little ones go for peanuts. Make sure you can plug it in and test the transformer before you buy it. Use a volt meter or ask somebody at the store or meet to test it with a locomotive. If you smell burning insulation, or if the throttle doesn't run smoothly through the whole power range, don't buy it.

You can probably find cheap rust-free used track at the same places. Don't forget to get a "lock-on" that clips the wire to the track. If you don't get one thrown in with the track, buy a new one--they're cheap.

Get some 16-gauge wire to connect the transformer to the track at the hardware store.

That's all it takes. I've used those techniques to restore trains that were 70 or 80 years old, and most of them run just fine.