I bought myself a 7 inch tablet when I was 8, and I used that as a smartphone. It was small enough to fit into most pockets, and looking at smartphones now, I guess I was just ahead of time with that screen size.
Yes, bought myself. It was the cheapest Android tablet, costing €50. It was quite a bit for me at the time, but nothing unrealistic. My parents didn't give me any pocket money, but you know, I had a grandma. She'd sometimes give me like 10-20 bucks and tell me to keep it away from my parents. And probably a similar amount in food each time I visited her xD.

As for internet, basically unrestricted access, and that turned out well for me. I'd be really (much more) dumb without all that access to information. Now, we didn't have internet, and we still don't (I am 18 now), so how? I've had a dumbphone before, with a SIM card of course. I could use 250MB for 50¢ for a day and top up the credit at basically any supermarket.
Obviously, that wasn't good for everyday usage. But there was something else. WiFi. Like half the people left WPS PIN enabled, with the default PIN. I then used app called "WPS WPA Tester" which had some 14 default PINs it would try. And it usually worked. Even if it didn't, 12345678 was a fairly common password.
However, I did understand that it's not quite good, so when I wanted to download something larger (>50MB), I went to places with public WiFi. Usually the bus station.

Social media: I've only used Facebook for a long time because my parents wanted me to have that (how ironic). However, I've deleted it when I was 12. Too much dumb stuff. I've seen some classmates use Snapchat, and I liked the filters. However I thought it was just a camera app, but when I downloaded it, I found it needs me to sign up. I've always had the same allergy to signing up on random places, so I quickly uninstalled it.
When I was 13 I signed up on Twitter and Quora. Twitter mainly for space-related accounts like NASA, SpaceX, Scott Manley, NSF,... and Quora occasionally had questions even I could answer.
At 14 I got my first laptop which needed an OS. I liked Linux Mint (and didn't even understand the difference between Windows) and Reddit had a nice community for LM. So I signed up on Reddit.
At 15 I signed up on Telegram for the PixelExperience community as I installed the PE 11 custom ROM on my Moto G5s Plus.
At 17 I created an account here on Lemmy, ditched Reddit (due to API changes), deleted Quora account and deleted the Telegram account.

Overall I think it was mostly positive. It allowed me to learn a lot and get in contact with more people. I wouldn't even know any English at all without it, which basically unlocked me the gate to most information. And now, I'd probably be mostly a copy of my parents, which would be terrible. Fun fact: The first website I visited when I got internet access was Wikipedia. So much information in 1 place.

But yeah, I should mention some negatives too. I did spend quite a bit of time watching Minecraft and FNAF videos. Although before the tablet I spent all that time with TV, so I guess not much difference.
I should also probably mention that until high school I didn't even take my devices to school because I was worried about them getting stolen or broken. I never broke a screen, so that was a success.