If they're not doing the work then I doubt they care about what got them hired. Ultimately each person should be judged on their own merits, I wouldn't hold a relation against someone if they still do their job.

Another question to ask... Is the person where they are because of their parents or in spite of them?

If a less qualified, young candidate walks into a higher position, and happens to have well connected parents. Yeah, I am going to default that they got the position because of their parents.

If the children of Jeff Bezos, Bill Gates, etc happen to materialize on an elevated position right out of college, are we to assume that they got their purely out of spite? Maybe they truly are brilliant and deserve the position, but they will always have had a leg up on the competition.

Your company will hire two people out of a candidate pool of 1,000. You're told that Well-connected Walter is one of those 1,000 and is guaranteed a job. Your hiring team is going to go through and interview the remaining 999 and find you the top candidate. After a month of interviewing, you are presented with your two new hires: Well-connected Walter and Meritocracy Mary. What are the chances that these two are actually the best two hires, rather than the best hire and a mediocre hire?