Answer:
The probability of having a child with this disease is still a 50% one
Step-by-step explanation:
The parents are wrong here supposing that their next child would inherit the autosomal dominant disorder gen.This could have well happened with their first-born but it didn't, and so it may or may not happen with their second child.
In an autosomal dominant disorder, there is one mutated gen that is dominant (it is located on one of the nonsex chromosomes). A person that carries a mutated gen has a 50% probability of passing this gen to their offspring. This is regardless of the number of children they had had before.