Of course, the vast majority of us didn't know anything about the Constitution before beginning to home educate. Most of us went to school in the government system - or attended private schools that simply imitated the system - where it's demonstrably irrefutable that kids have purposely not been taught constitutional truth for generations. That sounds nefarious, I know...but in this case it really is the truth.
Yet if we don't know our constitutional rights - and the strict limits the Constitution places on the government (because bureaucrats - up to and including the president - are public servants, not rulers) - we can be easily misled (i.e., "If you have nothing to hide, just let us into your home.") and abused. And, while retaining legal counsel is imperative after a bureaucrat has crossed a constitutional line - in fact, just hearing that a person has contacted a lawyer often causes bullies to go away because they know they cannot fool an informed person - we cannot rely on lawyers alone. Threatening situations happen quickly and when we least expect them. Thus, since we don't carry lawyers in our back pockets, we must know enough to defend ourselves - standing on our constitutional right to refuse entry into our homes absent a specific warrant, among other things - until we can make that contact.
Yes, Scripture is the most important document we have; every Christian home educator needs to be thoroughly grounded in the Word. But the Constitution runs a close second and - to paraphrase the Apostle Peter in a way I don't believe to be inappropriate - we need to "always [be] prepared to make a defense to anyone who asks...[why we stand on constitutional principles]" (1 Peter 3.15). It's not about being "mean" or "uncooperative." Rather, it's simply about compelling public servants - who are actually our employees, not our rulers - to abide by the law of this land. In fact, we are called to that by virtue of God having chosen to place us in America, where He has allowed for the Constitution - not government bureaucrats at any level - to be our authority.
Thus, please find a resource for educating yourself, and commit to making time for it now. One of my daughters is going through In the Constitution for her Civics credit; the other is using the Notgrass government materials. Of course, other good resources exist, too - for example, Hillsdale College offers a free online Constitution course for teens and adults - and The Homeschool Resource Roadmap lists well over 100 non-common core Civics resources. Whatever you choose, do something.
In 2013, at a homeschool convention, I heard a talk by Dick Morris, who said he's convinced it'll be homeschoolers who save this country if that's possible. That's because it's likely that homeschooling parents and home educated kids - along with a few self-educated others - will know our Constitution and our history well enough to stand against tyranny. I believe he's right. But in order to do that - and to protect our families from bureaucratic overreach at any moment - we must take responsibility to learn what our Constitution says and means.