The Wizard of Oz...
...was on at our local playhouse, so we went to see it with our two kiddies, then 3 and 6. We sat in the front of the circle, so we had a pretty good view.

As the wicked witch is menacing Dorothy in one particularly harrowing scene, youngest gets up and shouts at the top of his lungs "Stop doing that, you naughty lady!"

Cue whole theatre in giggles and the entire cast trying manfully (and womanfully) trying to stifle their laughter too, not entirely successfully.
( Amish Information Systems hates misplaced, commas, Fri 7 Dec 2012, 16:24, 3 replies)

I like this
one.
(username failed moderation, Fri 7 Dec 2012, 16:51, closed)

Ballet
As schoolkids we we taken to see a ballet at a local theatre, I forget which ballet it was, I think it was possibly a compilation of scenes form several ballets, I can't remember. What I do remember was that it was pretty boring to us little kids until during one scene a girl sat down on stage , opened her legs and placed a large football there and began to stroke it gently ( The ball I mean! ) Just then one of the kids from another school that had also been taken to see this stunning entertainment shouted at the top of his voice "OOH LOOK, SHE'S FUCKING IT". I think even some of the teachers giggled at that.
(Mackeson_drinker, Fri 7 Dec 2012, 16:57, closed)

The understudy
The most amusing production of The Wizard of Oz I ever saw was in 2001. Two brief moments occurred when Toto should have been visible on stage, but wasn't. That didn't bother me much - working on-stage with dogs can be difficult - and it didn't affect the show.

Backstage, the cast in a quandary. The irritable Scottish Terrier was biting everyone in sight; particularly Dorothy. Something had to be done.

At the end of the show, Toto reappeared. Except this time, Toto was a dazed-looking Dachsund/Chihuahua cross hastily seized from someone's back yard. Only in Oz!
(Perv With A Dog had his eyes pecked out by scrub jays on, Fri 7 Dec 2012, 18:04, closed)