If you decide to drive the Chicago route, you might need another 5 hours, ok, not that much, but, check for construction, they are always fixing the expressways out there. Those that know me, know I abhor driving around Chicago. Last time was mid Sunday afternoon, it was doable, just. Have change ready, toll roads! We ended up running one of the gates because signage was HORRIBLE, still no ticket in the mail, and it was August of 09.
You will probably average 50 miles each hour you drive, unless you drive way faster, way way way faster than your rig, and more importantly possibly your tires, are designed for. My opinion, is that first day is more like two horror days, 3 hard days (doable) and better yet 4 days, with a day off of driving in between day 2 and 3. But, we are old and retired, not young and employed, so fully understand your issues.
Good luck, have fun, smell the roses, and enjoy the kids, they will not be that young for long.