Hang on a sec. This move happened NINE MONTHS ago and Dad just noticed?!
I'm probably one of the least relocation-friendly posters here. But sometimes...well, sometimes the non-relocating parent just wants to be a thorn in the relocating parent's side. Now having said that, some places are VERY strict about relocation laws. Yes, you messed up - badly. But I'm not sure it's not salvageable.
Do you have ANYTHING from Dad - an email, text, anything - indicating he was fine with the move?
Can you show that the kids have been sent to Dad for visitation?
Other than that, a quick primer

:
States fall into one of these categories when it comes to relocation.
1. Presumption is against relocation - the relocating parent has to convince the court that the move is in the best interests of the child/ren. FL is an example of this.
2. Presumption is in favor of relocation - the NON relocating parent has to convince the court that the move shouldn't happen. WA is an example of this.
3. There's no presumption either way; both parents have to defend their reasoning. CT is an example.
Technically there is a sort of 3.5 category too - when the burden shifts. Indiana (go Colts even thought they're not my Steelers, coz we love a Manning. Except when I'm talking to cbg

) is a great example of this.
So with that said, Indiana falls into the "shifting burden" category. Not only is the burden of proof on Mom, but she failed to notify Dad and the court correctly.
While we can't guess what will happen - and I tend to fall into the "Well, the judge is going to be pissed but I doubt he'll punish the kids by uprooting them again" train of thought - OP really does need to high-tail it to an attorney.
You cannot mess around with child relocation. And Indiana made a really great pamphlet that comes in very handy:
http://www.in.gov/judiciary/center/...relations-custody-relocation-presentation.pdf