What if children were kept of social media?

Australia is planning to ban access to social media for children under 16.

Leaving aside the questions of "Is this a good idea?" "How can this be done?" "How will the world react?" "What should count as social media?" etc., I will ask a different question:

What should exist instead?

If you were to design a replacement for social media for children, what would it do? What would it do?

We understand something about what makes social media potentially harmful to children (and others).

What would actually make it beneficial?

I understand something about what needs to be removed, but don't know where to go from there.

If you have any positive ideas, please add them in the comments.

At the moment I am baffled.