Should I go on an interview if I don't want the job?

I applied to a bunch of different positions at two different hospitals a few weeks ago, because I was looking for a PRN job after being a stay home mom for 2 years.

Hospital A called me right away and I went in to interview for an L&D nights PRN job and I got the job! Yay! I'll start in a few weeks. L&D was my previous speciality and it seems like a great unit.

Hospital B just updated the status on one my applications that I'm being considered for an interview. It's Neuro med/surg. Honestly I don't have much interest in that area - I just applied because I was applying for anything that said PRN to get my foot in the door.
I'm interested in this hospital because they have a great children's hospital and I may want to switch specialities to Peds down the road and it looks they mostly hire internally for Peds.
But I don't know if that's a good enough reason to take a job I don't think I want.
I don't even know what I'd say in the interview if they ask me why I'm interested in that floor!

Honestly I doubt they'd hire me PRN for that floor when my only experience is L&D.
But I don't want to **** off HR since I may be interested in applying for a Peds position there at some point.
And I have an active application there for PRN NICU, which I doubt I'll be called for, but if I did, I WOULD like to interview for that one.

If they do call me, should I say I just accepted a PRN L&D position at another hospital and need to decline the interview? Maybe express interest in the NICU job while I have her on the phone?
Or just go on the interview and see what happens?
I would thank them for their time, explain you just accepted a position elsewhere.Normally I would say that going on the interview, even when you're ambivalent, is good experience. But if you just accepted a different job somewhere else and there's no chance you would take it, then you'd be wasting their time.

Quote from kloneI would thank them for their time, explain you just accepted a position elsewhere.Normally I would say that going on the interview, even when you're ambivalent, is good experience. But if you just accepted a different job somewhere else and there's no chance you would take it, then you'd be wasting their time.

The weeding out of applicants is usually such a long process that I think most HR departments are used to hearing that while they were screening, you got another job.