Gangchon Rail Park and Nami with 18 month old

Hello, we are planning to bring our 18 month old child to Gangchon Rail Park and Nami Island. We primarily want to visit Gangchon for the rail bike, scenery and relative ease of pedaling compared to some other rail parks.

I’m currently deciding between travelling by public transport vs private car. Which would be easier? Can diapers be changed on the trains or train stations/would drivers allow us to pause the journey to change diapers? I do notice that the journey is 1.5h by car vs 2h by public transport, but would the journey by car typically be slowed down by traffic jams anyway?

(I know many people would prefer getting a car for young kids, but our child tends to do long journeys better on trains rather than cars hence the question.)

If travelling by public transport, I’ve seen many guides saying to take ITX train. However on NAVER it says to take the regular metro with 1-2 transits, is that correct? We’ll be starting from our accommodation at Orakai Insadong Suites.

Finally, I’ve seen some comments that Nami Island isn’t as nice as the Garden of Morning Calm. Would it make sense to skip Nami and do Gangchon and the Garden instead? Or are they too far apart to make sense? I’m not ambitious enough to plan all three with the kid.

Thank you for your help!