Hello Sandra and thanks for bringing such a great question to the Disney Parks Moms Panel.
I don't believe that currently there are any methods as you mention of identifying a child's height for the purpose of enjoying Attractions at Walt Disney World Resort; other than measuring the Guest on site and by utilizing the keen eyes and great judgement of the Cast Members!
Each Walt Disney World Resort Attraction that carries a height restriction has a measuring stick/device at the queue entrance and again before actually boarding; Cast Members are always on hand to assist and will be happy to measure your child for you.
But as I previously mentioned Cast Members seem to be extremely skilled at identifying children who appear to be too small - just by looking at them!
Walt Disney World Resort and all it's lovely Cast Members are simply
Wild About Safety; so always follow their good advice!
When our children were little we used to measure them at home before our trip to Disney, purely as a guideline so we knew what to expect; it's possible to check out each Attractions height requirement
here. Have you heard about the
Rider Switch Service? This super system allows Guests to remain together as a group even if one Guest does not wish to ride or is too small to enjoy an Attraction.
For some wonderful further information you may wish to check out
Planning for Pre-School Kids & Little Ones. I'm sure your little princesses will have a magical time at Walt Disney World Resort making memories which will last them an entire lifetime.
Have a great Disney day.
~ Jane