If you see a person with a disability or facial difference, please do not tell your children not to say anything.

This teaches them that we should ignore people who are different.  When a simple question and answer will help them understand they don't need to be afraid.

So, instead, say that yes, there is something different about that person, and that is OK!  If it's appropriate, ask the person or the parent about it.  I feel sure they prefer that, than staring and pretending they aren't there.

When kids have asked me about why Emma seems to be staring at them and I explain her eyes don't move or blink like theirs, they say "ok" and move on.  Otherwise they might dislike her because she seems to be rude or aggressive.

We see children (strangers) watching Emma, glaring at her because they can see a difference but maybe don't know what.  They may assume she has lower intelligence or is unhappy.  They avoid her and ignore her when she tries to play with them.

Oh, how I wish they'd just ask.