Hi Elizabeth,
I am pleased to tell you that there are many rides which your Grandchild (at 1 metre tall) will be able to enjoy during your next visit to Walt Disney World.
There is a tool on the Walt Disney World website which gives a list of all the attractions which children of certain heights can participate in which can be found
HERE
If you look at the 'Narrow Your Search' bar on the right hand side of the page, and scroll down to 'Height' you are then given the ability to tick the height of your Child. Once you have done this, the list of attractions will be altered so that it only shows those attractions for which the Child in question meets the height requirements.
If your Grandchild is 42" (102 cm) tall when you next visit there is only a handful of attractions which he/she will be unable to ride which include:- Rock 'n' Roller Coaster at Disney's Hollywood Studios, Mission: SPACE at Epcot, Expedition Everest at Disney's Animal Kingdom and Space Mountain at Magic Kingdom.
I hope that you have a magical trip!