Is the feed algorithm the only problem that is harming children? Not the concept of a social network in general, the entire point of whose is to publicise lives and keep its users stuck onto their screens for as much time as possible?

The entire fault of social networks is that it is hampering children's development by keeping them online. Trying to improve those services by making the algorithms better will worsen the situation. You want to make children lose the appeal of social media, not increase it!

I agree with where you're coming from, but publicly documenting their feed algorithms (which is what a call for "open source" effectively is) wouldn't change much. What is actually needed are open API access to the data models, so that competitive non-user-hostile clients can flourish.

I believe this would be legally straightforward by regulating based on the longstanding antitrust concept of bundling - just because someone chooses use to use Facebook's data hosting product, or their messaging products, does not mean they should also be forced to use any of Facebook's proprietary user interface products.

This would not solve the collective action problem where it's hard for an individual parent(/kid) to individually reject social media, but I also don't see this bill doing much besides making it so that kids have to make sure their fake birthday is three years earlier than the one they already had to make up due to COPPA. Of course the politicians pushing this bill are likely envisioning strict identity verification to stop that, but such blanket totalitarianism should be soundly rejected by all.

Unfortunately the larger problem here is that the digital surveillance industry has been allowed to grow and fester for decades with very few constraints. Now it's gotten so big and its effects so pervasive that none of the general solutions to reigning it in (like similarly, a US GDPR) are apparent to politicians. It's all just lashing out at symptoms.