When social media started to take over the internet 20 years ago, it was widely hailed as a game-changing technology that would connect people across divides and make information more accessible.

Today, companies like Meta, owner of Facebook and Instagram, Google, owner of Youtube, and Snapchat, along with relatively newer platforms like TikTok, Discord and social gaming platform Roblox, are facing thousands of lawsuits in the US over claims that they have instead harmed users, children in particular.

Taken together, the outcome of the lawsuits, whether they ultimately settle out of court or end up with jury verdicts against companies, could change the way social platforms operate forever.

"It's created a stage that not only legal observers are watching, but regulators and lawmakers are watching closely as well," Eric Talley, a lawyer and professor at Columbia Law School, said.

Talley noted that the way this growing wave of lawsuits against platforms is feeding into broader public perception is likely to influence political elections for the next several years, impacting new and revised laws and regulations.

Many of the cases are going through courts in California, where all of the major social platforms are headquartered. Known as the "California effect", legal and policy changes enacted in the state tend to lead to nationwide changes.

"There's no denying anymore that there is an issue with child safety on the platforms," Alexis Shore Ingber, a communications law expert and a professor at Syracuse University, said. "We are seeing an inflection point. These cases are significant."

Already this year, Meta and YouTube notched an unprecedented loss in a case brought by a young woman who claimed she was addicted as a child to social media, contributing to her mental and emotional health struggles. The companies were ordered by a jury to pay her a combined $6m (ยฃ4.5m) in damages. Both firms said they disagreed with the verdict and intended to appeal.

Meta also lost a bigger case in New Mexico, brought by that state's attorney general accusing the company of essentially misleading the public that its platforms were safe for children despite known issues with young people being sexually exploited on them. Meta said it also plans to appeal against this verdict.

During the years these cases were brought and resolved, Meta has released changes to its platforms aimed at making them safer for young users.

But broader change to the platforms, how they are designed and function and even accessed, is likely to take years more, and more court rulings against them.

Between this year and next, Meta and the other major social platforms are poised to fight their way through more trials where juries could consider a host of claims by young users, their parents, school districts, and state attorneys who allege an array of ill effects from the way social media platforms are designed and operate.

Even a billionaire is prepared to take Meta to trial over its hosting of advertisements that scam people out of money.

So which cases really matter?

The BBC looked through scores of cases in the US to find the handful of lawsuits against social media and social gaming companies that are on track for trial in the next year or so and could have a significant impact on the platforms' businesses and operations.

According to Adam J. Schwartz, a lawyer who also founded an online document review tool, the following lawsuits "are the bellwether cases that will set the tone and tenor for shaping the law in the future".

This sprawling multidistrict litigation (MDL) in California includes allegations from more than 1,000 school districts across the US.

Broadly, the schools accuse Instagram, YouTube, Snapchat and TikTok of being intentionally designed to be addictive, which has allegedly harmed children mentally and emotionally through their excessive use of platforms.

The schools claim that dealing with the ill effects of social media has cost them money and resources, and that the platforms should be deemed a "public nuisance" and held liable for impacting children's well-being.

Although a jury trial for certain of the school districts' claims is now set to begin in February, as the platforms recently settled with a school district that was to be the first trial, all of the cases could take a couple more years to resolve completely.

Should court outcomes go against the platforms, everything from the way platforms display user engagement to who they allow on the platforms could change.

A spokesman for YouTube said: "The allegations in these complaints are simply not true."

A spokeswoman for Snapchat said: "We fundamentally disagree with the allegations - we do not target schools."

Meta declined to comment and TikTok did not respond to a request for comment.

Attorneys for California and Colorado led a group of 29 states in filing in 2023 a lawsuit against Meta and Instagram. It is set to go to trial in August.

While it is also before the same judge as the MDL in California, the states are accusing Meta alone of violations of the Children's Online Privacy Protection Act, a federal law known as COPPA. The law was intended to protect children under 13 years old from being targeted by businesses operating online but was enacted in 2000.

Meta has already provided more than 2 million documents in the case, according to court records.

Should the states prevail in their claims, it is demanding that Meta better prevent users under 13 years old from using its platforms and remove data it has previously collected from underage users, along with a host of other changes.

Meta uses such data to do things like ad targeting and train its artificial intelligence (AI) models and tools.

A spokesman for the company declined to comment.

This case against Roblox and Discord was brought by a 13-year-old boy in state court in San Mateo, California. The boy claims he was recently groomed and solicited through both platforms by an adult sexual predator who was subsequently arrested for his crimes against more than two dozen children.

The lawsuit argues both platforms were defectively designed and engaged in false marketing about safety for young users and so should be held liable for the harm young John Doe came to.

Roblox, which is a gaming-focused platform with many social media features, and Discord tried to get the case into arbitration, which is a private legal process outside the court system. The court refused, but the case is currently on hold pending the companies' appeal against that decision.

Should Roblox and Discord lose their appeals, the case could go to trial later this year. A court verdict against the platforms may bring changes to age-gating and the ability of strangers to interact with young users through platform messages and chat spaces.

A spokeswoman for Discord declined to comment. A representative for Roblox did not respond to a request for comment.

Not all of the cases against social media platforms heading towards trial have to do with harms against children.

Dr Andrew Forrest, an Australian billionaire, sued Meta in California in 2022 over the company's alleged failure to combat scam advertisements tricking Australians into fake investments that allegedly proliferated on Facebook using his name and likeness.

With claims including misuse of his image and unjust enrichment, because Meta makes money from ads on its platform no matter their goal or outcome, Forrest's lawsuit could be one of the most significant.

He is asking the court to find that Section 230 of the Communications Decency Act cannot be used as a defence by Meta in the case. Meta is arguing that it is protected from Forrest's claims by Section 230.

Enacted in 1996, Section 230, as it's usually referred, essentially gives legal immunity to platforms for anything that occurs on them.

If the court ultimately sides with Forrest, it could upend decades of defences by online platforms.

A spokesman for Meta declined to comment.

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