Start your kids touring with you at a young age. Ideally, figure out how to get your spouse interested in it, too. I have an 8 year old son, and we've embedded biking, hiking, and even bike touring in many (if not most) of our vacations since he's been born. From a three day trip on the C&O Canal with him in his Burley trailer behind our tandem, to a self-supported bike tour along the Danube last year on our triplet bike (three-seater). My wife also enjoys touring, even though she's not an "athletic type." BUT, we tour the way that works for her: on our own, but staying in B&Bs, hotels, etc. Maybe someday she'll want to bike across the USA with me, camping mostly, but maybe not. That's ok.
Partnerships are about meeting in the middle. Find a way to make it work and be fun for all involved. It's not just about what you want!
But back to the original question: for every person that takes three months to ride the Transam, there are probably 5-10 of us who have done an overnight tour, or maybe a week or two tour. They aren't as sexy as the long-haul tours, but are good for the soul nonetheless.
This summer I took a month off work and we took our campervan across the USA (with bikes on the back :-). #1 question we got was "how did you get so much time off?" Simple: I asked (and took all my vacation time at once). Not everyone has such an understanding manager, but you don't know unless you ask. I took my work laptop with me, checked e-mail each day, but thankfully didn't have to do much troubleshooting at all. I felt like I was being responsible to my boss and colleagues, though, by being available if needed.