Hi Photonic,
congratulations to you and your son for the extraordinary accomplishment.
There will be no record of anything similar; the park authorities only record basic statistics (in those big paper books), and as far as I know nobody else gets any statistics.
It is also quite hard to define 'disabled'. Technically somebody with glasses is also disabled and there might have been other young persons with some kind of disability.
I think that it is quite safe to say it, but maybe you can disclaim it a bit by adding 'as is currently known' or something. Another option might be to contact Guiness book of records, they might know more (though they might contact me again

)