Repairing Replacing Broken Wires

We have several Tomy trains, Thomas steam along, Gordon, Edward we bought at a used toy sale with broken wires between the engine and coal car/Annie.

Is it worth trying to repair them? If you did repair the wire, how did you do it?

There doesn't seem to be enough wire to splice together.

I have a roll of speaker wire and electrical solder. Will that work for replacing the black and red wire?

Thanks