There are some parts of this movie where laughter would have been inappropriate. However, this is just silly on the part of the theater manager. You don't tell parents to park their handicapped children at the curb and return to the movie.
But since this guy is your fairly typical movie theater manager, this is not surprising.
If it really were impossible to continue to run the movie under those circumstances, the theater should have offered the family a private screening. That way the customer is happy, the other patrons are happy, and your theater staff does not look like a bunch of ignorant goons.
offer the family a private screening A fine suggestion! It would solve the problem all around, and the manager wouldn't have a lawyer breathing down his neck for violating the ADA. (He could throw in free popcorn, too.)