Best place in MA to see trains crossing a diamond is in Palmer off the Mass Pike just east of Springfield.
Very interesting move by the Amtrak Vermonter to switch from NE Central to CSX tracks in addition to good amount of freight activity.
Steaming Tender restaurant is in what used to be the Railroad Depot. GPS 22 Depot Street Palmer MA.
Your Grandson rode on the North East Corridor Tracks which see freight activity only by the Providence and Worcester Railroad in CT and RI. You can see the P&W every weekday around 12:30 in/around Old Saybrook CT where two trains exchange cars, one to head north to Worcester and one to head south to New Haven
Paul