This is a very tricky situation. The chances of you bringing the children back is extremely unlikely. That is why we suggest a legal separation in which a parenting plan because you can put in the agreement that she can not take the children out of state without your permission. Once she has moved it is very difficult because you are dealing with 2 different jurisdictions now.
As far as visitation, you will want to file with the state where the children reside now. In this situation most non-custodial parents will get summer vacation and holidays and since she moved without your consent, they may make her pay for their transportation.

