The toe ring test probably wouldn't fly, the Ministry detects underage magic outside of the vicinity of Hogwarts and responds harshly.
In canon, the detection spells can't even tell the difference between Dobby's use of magic and Harry's. Telling the difference between a kid's magic and his parents' would appear to be even harder. For the wizarding kids, if their use of magic can't be told apart from their parents, there would be no way to sanction them. At that point the detection spells are only effective for muggle-borns. I'm not aware of any in-canon detection of children living with magical parents. (This would also let the wizarding families train their kids even when not at school, as a convenient way to bolster their status).
Update: Discussion has moved on to a new thread.
The load more comments links are getting annoying (at least if you're not logged in), so it's time for a new Harry Potter and the Methods of Rationality discussion thread. We're also approaching the traditional 500-comment mark, but I think that hidden comments provide more appropriate joints to carve these threads at. So as of chapter 67, this is the place to share your thoughts about Eliezer Yudkowsky's Harry Potter fanfic.
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six. The fanfiction.net author page is the central author-controlled HPMOR clearinghouse with links to the RSS feed, pdf version, TV Tropes pages, fan art, and more, and AdeleneDawner has kept an archive of Author's Notes.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: