You came to the right place. Lots of railfans are also amateur radio operators, myself included.
I think if your son has an interest in weather spotting, a dualband handheld radio would be a nice gift. Some of the Skywarn weather nets use both 2 meters (144-148 MHz) and the 440 MHz bands. Likewise, if he becomes involved with any disaster response groups such as RACES or ARES, the ability to talk on either band may be useful. All depends on the area. Some groups use 2 meters exclusively. One advantage of a dualband radio is the wideband receive capabilities well beyond the amateur radio bands. This may be helpful for listening to police and fire, but that depends on the specific agency and whether or not they use a trunked radio system. Amateur radio handhelds are useless for monitoring trunked systems, even if it's capable of receiving the frequencies used. Trunking scanners are widely available for this purpose if your son wants to listen.
The Yaesu FT-60R is one of the cheapest dualband radios available at about $160, but it's also a rock solid performer. I wouldn't hesitate to buy another one. I would stay away from the Yaesu VX-3R. Nice radio but not appropriate for a first time user and it doesn't put out 5 watts in transmit mode. The Yaesu VX-6R is a nice dualband radio for about $290. Has more functionality than the FT-60R.
I'm not familiar with the latest offerings from other manufacturers, such as Icom or Kenwood. Hopefully somebody else can chime in here. Additionally, if you are willing to tell us your son's approximate location, we might be able to tell you if a dualband radio is appropriate or not.
Feel free to e-mail with any questions:
david@altamontpress.com
David