I need help with an interview talking point that I know they will ask.

My entire career (except I have a music degree and a songwriter side thing, which is irrelevant here)
has been as an admin, reception...I've done everything plus I'm microsoft certified in Word, and could be in Excel if I took the time..
so that gives you a little bit of my background. I also did 2.5 years in recruiting before the economy tanked so I'm good with the resume thing and I know how to interview...he's the deal though:

Without going into the long explanation why...other than it was what I could find at the time (mostly true, but other reasons as well),
I've been working as a preschool teacher with 0-5 kids for the last 2.5 years. I love working with the kids and it was nice not working in a cube for once and there are other good aspects to the job. But the physical part of it is really getting to me. I'm only 40 and I've never had some of the problems I've been having physically. Plus we are expected (even though they don't say it directly and won't...but it's implied and expected) to do some of our own administrative work at home. We are given only two hours a week, and it's just not enough time. I probably spend at least 4-10 hours a week working on lesson plans and putting in observations or working on things for the class room with my own printer and ink, etc.... I can't say whom I work for but it's not a private school or ISD, and I'm not going to be able to change the system. What I can do is get off my feet at the same location with a desk job instead.


There is an position open at the front desk, it's an admin job. I worked for 2 years part time until I could get on full time as a teacher. I had interviewed for the desk position in August, but someone else got it...then I interviewed for an open full time teacher slot in September and landed it. They pay the same, by the way...I just need off my feet and don't want to work off the clock.

This front desk position opened unexpectedly. I will be submitting my resume, and I will probably get called for an interview.
It's possible they won't interview me, but I think they probably will...

anyway, if you've read this far...my question is this:

They will probably ask why I'm interviewing for the desk job since I've only been full time for 6 months.
I got the health care I needed with the full time teaching slot...but now I need off my feet.
I know (duh) that I won't be telling them I need to get off my feet.
So, I know they know I interviewed before because they are the ones that interviewed me...
so they know there is some interest in the front desk spot....

but what should I tell them, in answer to their question, in why do I want the front desk job.