I agree. I took a 9 YEAR hiatus from a career. I described it pretty similarly as others have said..."I stayed home due to family needs at that time" then was certain to mention casually that all was well now. I figured it was none of their business what was happening when it didn't impact them.
I don't see any reason at all to bring your son's situation into any of the interviews. If need be, when the offer is being made and only if you won't have vacation time available, you can tell them that you will require a few unpaid days off in March (or May or whenever) because you've previously made a commitment that you have to honor. Period.
Suz
