Not far from the Wulai hot springs is the station for the Wulai Tourist Railway line. Follow the sign for Helen Coffee (which is incidentally a very pleasant spot for a relaxing cup of coffee) then you will spot the rail tracks.
The rail line was previously used for transporting timber out of the valley. Nowadays, the railway only transports tourists.
Kids will probably enjoy the train ride, but it is also quite a useful transport link to connect you between the hot spring area and the Wulai Falls.