Japanese website on Tateyama Kurobe Alpine Route mention following regarding small children on Frequenty Asked Questions section. I think it is important to note that Tateyama Kurobe Alpine Route was completed in 1971 back when access by wheel chairs and such was not considered, it was early ‘70s in Japan, you know...

• Route has elevation difference of 2000 m (6,500 ft.). Some elderly and young children do have more difficult time adjusting compare with healthy adult.

• Can bring strollers onboard buses, ropeway, etc. However, there are many transfers and walking route has many stairs. Which make strollers particularly not convenient.

• Bus ride between Bijodaira and Murod is 50 minutes ride, buses do not have toilet onboard and there is no facility between Bijodaira and Murod.

• Bus route has a lot of sharp curves. Elderly and younger child tend to be more susceptible to motion sickness.