How can I block with a child theme certain pages?

Those page are just traditional pages in your WP backend. Each with a shortcode for content. So you could delete those pages or switch them to un-published or private. I don’t think you’d need to delete any theme templates.. which don’t exist anyway for things like “cart”, “checkout”, etc.

If that doesn’t do it, consider the extension. If you spend more than 1-2 hours figuring this out, then the extension will have been worth it.