Message boards like AFF and Whirlpool and Reddit absolutely fall under the definition of social media(they are an online forum where people have social interactions); they are in fact amongst the earliest types but just not super popular with todays youth. Likewise platforms like Facebook now skew to 40+ and aren't cool enough for tweens.
I dont have kids, but if I did I would have a dialogue re usage and not ban it. If your kid has android phone/tablet is very easy to use parental controls to set time limits, block certain sites. My best friends husband was admin for their 3 kids phones/tablets goin back to the 2010s; they had to earn screen time by doing their chores (he could remotely lock them out, limit them to school website until homework was done etc); turn off the wifi remotely.
I've been online since I was a teen in the early 90s back when it was all text based bulletin boards, then IRC then later windows ICQ, browser based message boards, geocities communities etc overtime people move to new platforms. My parents didnt understand the technology, had no idea who I was talking to, but a little common sense goes a long way.
Teen suicide is awful but I seriously doubt social media is the sole cause (an it existed well before socila media you just heard less about it). I imagine those kids are also being ignored/snubbed or bullied in person at school too; or experiencing abuse or other issues. You can ignore what people are saying about you online, but its more real when you have no one to have lunch with, or no one wants to work with you on a group assignment, or are taunting you on the bus etc.
There have always been been bullies in the real world and online. Take away access to social media apps and kids will find another way; they will likely still have phones (parents seem to think its essential) so can use sms, resort to old school behaviors like nasty notes in your locker, rumour spreading, ignoring, name calling, not inviting the weird kid to parties etc.
There will also be a negative unintended consequence for many kids who dont fit in at school; they will lose opportunity to find their community/likeminded friends online and therefore lose an element of support which may be the only thing helping them to survive the nasties at school,
Kids of course will use an older siblings/friends account or use false credentials to circumvent controls.
Its a slippery slope asking overseas based social media companies to verify identity. Who is seriously going to be stupid enough to give any site like Facebook or even AFF visibility of sensitive personal data like ID documents to prove age? Australia doesn't have a national ID card; and given the glitches with my.gov.au basic functions their platforms aren't sophisticated enough for 3rd party social medias companies to validate your age via it. Noting that few under age 15 work, so wouldn't even have a my gov account.
Education not censorship is the answer.
Would pefer the government focus more on requiring social media to better vet fake news / deep fakes, and forcing platforms to remove unauthorized content (i.e. when bullies/scammers create fake nude images or post real ones gained by hacking) in timely manner.
Finally parents should think before posting images or anecdotes about their kids online. Your baby cant give consent, but that baby will grow up and may be mortified you posted so embarrassing image/event online.