Earlier quoted context omitted.
You can't keep them off it. If you don't provide them access, they can get access on their friend's devices. The key is education, you have to explain to your kids how these services works, how they are optimized for content engagement to show ads, how they mine your data, and what kinds of things they should look out for and avoid (like misinformation, catfishing, grooming, viral stupidity etc)
As if an 11-year-old will absorb any of that...
I have an ongoing conversation with mine about the things he finds online. We talk about how people try to benefit from appearing "rich" online. We talk about how people have problems in their lives and find things to blame and rant about online. We talk about how people you don't know can try to get things from you or make you think a certain way.
He even started using the term "clickbait" before I even taught it to him. These kids are savy. I think the biggest thing we can do for them is to help them understand how to contextualize what they're engaging with because they don't get to grow up in the "before" and "after" worlds that elder millennials did.
And frankly, I see that my kid is just as saturated in propaganda from his public school as he is from online media. So far, in parallel to his education, school seems to be running one giant ad for the US armed forces.