(CNN) – A Pennsylvania roller coaster remained closed Friday, after the fourth amusement park accident in the U.S. in a matter of just five days.

Investigators are trying to figure out how a three-year-old boy fell off the ride known as “Rollo Coaster” at “Idlewild and Soak-Zone” park outside Pittsburgh.

The incidents have many wondering ‘who regulates amusement park safety?’

The week ended with an accident at an amusement park in Pennsylvania – a three year old boy, injured when he was thrown from a roller coaster.

And it began horrifically with the death of 10-year-old Caleb Schwab, whose neck was broken after he was tossed from his raft on the world’s tallest water slide in Kansas City, Kansas.

Rider John Powell said, “We found out what happened and we were just sick, thinking ‘oh my gosh’, the same thing happened where the raft went airborne – and this young little guy was killed.”

Every year, more than four thousand children are rushed to emergency rooms because of injuries at amusement parks. From May to September, 20 children on average everyday are rushed to the ER, according to a study from Nationwide Children’s Hospital.

The study’s senior author calls for a national system of regulations to “prevent amusement ride-related injuries through better injury surveillance and more consistent enforcement of standards.”

What? There are no national standards? No federal body making sure these rides are safe?

That’s right. The federal government used to regulate safety of amusement parks such as the one in Kansas City. But in 1981, amusement parks at standing locations suddenly became exempted from regulations – a loophole inserted, its critics say, without any deliberation or debate.

Complying with federal regulations costs money, and though amusement parks are a $12-billion a year industry, leaving it up to states is better for their bottom line.

Jim Prager was a senior executive at Six Flags who helped fight to create the loophole in 1981. He was also a board member of the International Association of Amusement Parks and Attractions or IAAPA.

Prager told CNN….he was wrong. “Children are not well served by the law as it now reads. We haven’t done enough to make rides safe and we should do more. Amusement parks don’t want regulation because it costs money.”

In 1999, then-Congressman, now Senator Ed Markey of Massachusetts began a crusade to push a bill to close the loophole so amusement parks would again be covered by one set of rules and regulations. “That loophole is responsible for situations where major accidents are occurring in huge amusement parks across the United States. Because of that the federal government is prevented from investigating accidents at amusement parks, sharing accident information with operators of same rides so malfunctions can be fixed, requiring manufactures to correct design flaws, and enforcing a full range of safety measures on amusement park rides.”

Since around the time Markey began his crusade in 1999, the IAAPA spent more than $11-million lobbying against his bill, among other items, according to the Center for Responsive Politics.

The IAAPA hired a pricey lobbying law firm in D.C., Williams and Jensen, which represents many different businesses, and whose members and affiliates have poured more than $7-million into campaign contributions.

IAAPA declined our invitation to talk, but its website says “states are best equipped to regulate amusement park industry.”

Oh, really?

Let’s look at Kansas, home of the Schlitterbahn Water Park where Caleb Schwab was killed this week, and where regulations are, according to experts, minimal.

The opening of this ride, where Caleb Schwab was killed, was delayed several times due to safety concerns. After it opened in 2014, how many times did the Kansas Department of Labor inspect the ride?

Well, zero, according to the Topeka Capital-Journal, which filed an open records request this week.

Prater says, “I believe some of the horrific accidents that continue to occur could be avoided if there was more regulation.

The last time Markey introduced his bill, IAAPA President and CEO Chip Cleary released a statement opposing it, saying the “industry is already safe and well regulated.”

The family of Caleb Schwab might disagree.

In a statement, the waterpark said, “Safety is our top priority at Schlitterbahn. All rides are inspected daily before opening.” The park passed a safety inspection back in June, conducted by an insurance company that the water park itself hired.

We should note we also heard from the Pennsylvania park where the three-year-old was hurt. It says nothing like this has ever happened in the ride’s 78-year history, and its roller coaster is inspected daily before opening.Copyright 2016 CNN