Snapchat is the focus here because it's better-suited to exploitation than the others you name as part of its design and marketing. But yes, there are also clearly issues outside of Snapchat as well.
people think snapchat images are 'deleted', yet that's not actually true, and can be intercepted/recorded anyway.
I don't know, I got by just fine with a dumbphone through high school (beginning of the iPhone era). I don't think most teens need smartphones, honestly.
But we've crossed the point where that matters.
In today's schools, some teachers plan activities where students use their smart phones for specific projects, so this is becoming increasingly harder to do.
Teach your kids better. There are several factors at play here. One is the technological ignorance you mentioned. Kids don't understand caches, archives, downloading media? Teach them. It shouldn't be hard to explain those concepts at a level that will allow kids to make better choices.
Another thing to teach kids is about anonymity, falsehoods and trust levels. You want to connect to your friend Michael on Twitter? When you next meet him in person, ask him for his username and give him yours. Anyone you randomly "meet" online might not be who you think they are or who they say they are. You don't have to automatically assume someone is hostile, but never automatically assume someone is benign.
Above all, don't give your kids means to get themselves into serious trouble until you've taught them. That means that if the kid is too young to properly understand these things, don't give them a smartphone. If you wouldn't send a toddler to walk alone to preschool a few blocks (and pedestrian crossings) away, why would you give a 10 year old a smartphone?
Most adults don't really understand these things.
Also have you ever parented a teenager? Some are less troublesome than others but most will do what they want to do, regardless of what the adults in their lives tell them to do. They are actually individuals that way.
That's what I feel is the hardest thing about parenting: coming to terms with the fact that you cannot guarantee nothing will ever happen to them. You have to try your very best, but there's no guarantee.
As for adults not really understanding these things, that's also an education problem. We can't just shrug and say that nobody really understands this, therefore educating people isn't really a solution.
Not a complete fix, but a service like snapchat specifically could use AI to block seemingly-nude photos for underage users. Perhaps it could offer parental oversight features too (though this would be hard to implement w/out teens flocking to fake accounts).
The drawback with this approach is that if it becomes mandatory (due to public pressure, legal risk, or legislative risk) it will work work to exclude startups from entering the market.
1. Trying to guard against the problem: assume anything on the internet will stay there forever, and will be public
2. Assuming the inevitable and mitigating possible damage: recognise that everyone does and can look stupid when they're naked - ie teaching kids to have a healthy body image and self-respect.
This idea that images in Snapchat are temporary and therefore of little consequence is not a bug, it's a feature. It's the defining feature of Snapchat, the reason for its success, and they absolutely positively captured a large chunk of their marketshare based on the idea that young people could exchange risqué photos privately on Snapchat like they could nowhere else.
When a platform is built on marketing something horrifying, I don't think we need to feel any responsibility to come up with an alternate business plan for them. I don't have suggestions for Altria Group either, other than just: stop selling cigarettes and go out of business.
Enforcing a minimum age of 13, and actually trying to enforce it, would be a good start. Using the ML tech they're so proud of to recognize nudity in photos and popping up warnings, including refusing to send photos if there's a chance the sender is a minor, would be a good start.
But really, just shut it down.