Would get thrown out before it went to court. Sued for what? A child may get sick?
All that has to happen is one child gets sick after playing on the swing set and the parent believes that the poison on the swing set was the cause. School districts here in CA would never, ever, use PT wood in a location where a student could touch it.
I can see from your comment that you don't have much experience with civil suits, and you should be grateful. What you describe, while apparently rational, does not happen. What really happens is the plaintiff files a suit, the defendent contacts his insurance co, and they negotiate a settlement. The more likely the suit has merrit the larger the negotiated settlement, but the insurance company will almost always settle prior to a trial because they, and their attorneys, know that the outcome is a "**** shoot" (their words). Insurance companies will almost always pay a known fixed amount now rather than take the risk of a trial.
I have personally seen situations where mold is discovered in a building and several people get sick. Most were not sick until after the mold was discovered though they claim they had been feeling "off" for months. Disability claims follow. I have have seen a school district test indoor air quality and as a result people claim illnesses. The actual tests showed no air quality issues. It was the presence of the testing people that caused the situation. Often a single claim precipitates several others as this explains why they had been feeling poorly or had arguments with their spouse.
These are, for the most part, not dishonest people however they are susceptible to suggestion.