I didn't know about falling off the membership at 18 without having signed a declaration, and will check on that to verify it, perhaps by sending a letter to National....
As I said, that was "my understanding" but now I'm wondering whether you might be correct. Can't offer you a link but did locate a pdf copy of a letter dated January 26, 2007 from the Regional Baha'i Council of the NE States. In part it states:
“Upon attaining the age of fifteen a child becomes spiritually mature and is responsible for stating on his own behalf whether or not he wishes to remain a member of the Bahá'í community.” [From a letter written on behalf of the Universal House of Justice, December 12, 1975]
When we know the number of children and junior youth residing in a cluster, we can ensure that children’s classes and junior youth programs are made available to support the needs of these precious souls entrusted to the care of the entire Bahá'í community.
While reinforcing the italicized directive from the Universal House of Justice, the second blurb seems to indicate the primary reason for enrolling children of Baha'i parents. Might be a good idea if you did write to National for clarification, not only because there are differing opinions about it, but it might now also bring into question whether non-registered children above a certain age may attend conventions (where ID is required).
so I just fired off an email to national asking them how a registered youth is NOT inheriting the faith of their parents.
Regarding your first question, it is incorrect to say that Bahá’í children who are registered as Bahá'ís by their parents automatically inherit the Faith. This is because at age 15 when they receive a Bahá'í membership card, each are clearly given the choice of accepting or declining the card. In accepting the membership card, the youth affirms his or her belief in Bahá’u’lláh. Further information concerning this topic can be found in Guidelines for Local Spiritual Assemblies: Developing Distinctive Bahá'í Communities (chapter 6, page 17), which is available online at the U.S. Bahá'í Administrative Website, usbnc.org"
and I'm guessing I should should have included an example from real life...
a nationally recognized Baha'i in my community had a daughter who, for whatever reason, never knew that a declaration card had been sent to her.
when she later discovered she is on the rolls as a registered Baha'i she was fit to be tied that, with no action on her behalf the Baha'i Faith mistakenly thought she joined.
in effect... she inherited the faith of her parents and was extremely displeased to discover it.
can't decide if I should send this example to National, it's not going to change my decision not to register my son depriving him of the exercise in free will to sign his own declaration card.
the good news is that my original letter to National has successfuly resulted in my (then) officemate and his family being removed from the covenant breaker list.