Thank you all for the wonderful advice.

Just got back from Tokyo and wanted to share, despite the warnings re. the platform transfers within the various stations - we found them to be very manageable, and well signposted. Nothing too dissimilar from getting off the Airport Express in HK Station and making your way to the Island Line.

- We took the Skyliner from NRT to Ueno, then to Hatchobori and finally changed to Maihama. Thought this would be a major hassle at 8pm but we were safely at our hotel by 9:40pm.
- Managed to ride the Asama and the Max Toki trains in Green Class - short but nice rides anyway for my son.
- Took the NEX back to the airport from Tokyo Station which was an easy connect from Maihama.
- Did a loop on the Tokyo Disney Monorail as well, and managed to buy him the Plarail version of the Monorail from the Disney Store.

All in all, a much easier trip than i anticipated.

Next he wants to sit in the front seat of the Romance Car to Hakone (he saw a picture of it in a Japanese Train Book i bought him!).