Sorry that I didn't get to answer this question sooner, but I've been off Disboards for 2 months (exactly) due to a silly thing called Life getting in the way (making a mental note to get my priorities STRAIGHT finally!).
First of all, everybody here did a WONDERFUL job of providing the answers that I would have given if I'd been around. I'm also glad that the article on Allears is useful. I'm actually the author of it & while it hasn't been updated recently, it IS something on my "to do
SOON" list!
As for the LMA Show, I would unfortunately have to say that if your grandson suffers from anaphylaxis due to latex, I'd have to recommend putting that show on the NEVER NEVER list. I went there once (I carry 2 epi pens, rescue inhaler, & Benadryl at all times) and while I did not suffer GREATLY, they also had to cancel a few of their "normal" stunts (including the finale with the big explosion) due to technical difficulties. Having never been there before, I admit, I foolishly never thought of the possibility of it being a dangerous show to WATCH; I've since revised my opinion and strongly encourage anyone with latex allergies to at least think long and hard about it and would recommend anyone who has suffered anaphylaxis due to latex allergies to stay away from the show at all costs.
From speaking with the supplier of those Mickey Ear Balloons within the outer clear balloons, I can unfortunately confirm the inner balloon is latex and as you can see from picture here:
there is a "tail" that does stick out and is exposed.
Unfortunately, no, Disney does not have to the best of my knowledge any policy about latex balloons per se. Unfortunately, it is up to the individual to be careful and responsible for themselves. One strong recommendation that I can offer is, if you see a balloon vendor up ahead, cross to the other side of the street/walkway/etc to put as much room between yourself and them as possible. Wind at WDW is variable... it has been known to blow the balloons (while still being held by the vendor) down to
ECV height, which may result in accidental exposure.
About the only other thing that I can recommend is that, aside from asking EVERY time you eat whether they use latex or non-latex gloves during food preparation (Disney owned restaurants generally use non-, but WDW cannot speak for the non-WDW-owned restaurants), also be assured that, should the worst occur and an accidental exposure happens, the Reedy Creek Improvement District Fire Department is exceptionally good and is ALWAYS located close by with PARAMEDICS who can and will assist. RCID Fire Department (who provides EMS coverage on WDW property) does NOT use latex gloves.
Any questions, please, ask away, & sorry to have been gone for so long!