I have elementary school kids both with special needs. It is important for people to remember just because a child "looks normal" you really don't know the situation ADD, ADHD, Autism, or underlying special needs like seizure disorder or certain types of sensory issues that can make waiting in extremely long lines tough. Also "holding it" is dangerous for everyone and some people forget to go until its a gotta go right now situation (Especially teachers and medical personnel) who habitually have to "hold it".
Now in my family it has become habit to not walk past a bathroom without everyone trying, however there are still those moment when 5 minutes later someone has to go

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I think the best way to think about things like the golden rule: Just ask how would I feel about ... and go with your gut. No one is going to please everyone 100% of the time.
Have a magical time and tons of fun!
Kris