My daughter had an iPod touch at 6, which she could imessage and facetime me on because I'm a single parent and the couple of days when she is with her dad, I work away. It really helped the transition that I could message her and she could send me pictures.
She's just turned 11 and earlier this year I got her an iphone on contract. It's insured but is also in one of those bomb proof cases (I use the same brand, I've a habit of dropping them in toilets...).
She uses whatsapp to talk to me, family and a couple of her friends. We had a big chat about TikTok, she had been asking for a long time and it's quite a big part of kid culture at the minute. We came to a compromise that she could have an account, but she had to have a private profile, could only accept people she knows, checks with me before she follows people and she isn't allowed to have her face in the profile picture or name in the handle. She also has Snapchat, but she only has me and her bestfriend on there and it's mainly used between us to use silly filters. Snapmaps is off.
I have an app called Find My Kids, you have that on your phone and you download the paired app on the child's phone called Pingo. It will show you where your child is, movement in real time and how much battery their phone has left. It also has a messaging function and an override so that if she's panicking or needs me urgently, she can press a button and an alarm goes off on my phone with her location, even if my phone is on silent. I thought it would need a bit of work convincing her to have it but she had zero problems with it. It'll stay on there until it becomes an issue, then we'll review.
She knows I have access to her phone whenever I need it and will leave it here while she's at school etc.
I think you have to judge how you approach this on an individual child level, I decided to have lots of conversations and be really open about social media and the pitfalls/warning signs and educate her. She knows that if anything makes her suspicious or upset or uncomfortable she can show me and I'll help deal with it without there being any chance that she'll get told off.
There's a benefit of pre teens having phones which didn't occur to me until it happened and that is if your child has a tendency to be a bit shy or not want to talk about something face to face, they will often feel much more comfortable messaging you about it. It has helped a couple of times when she's had body related questions that she hasn't known how to bring up face to face.