Just to clarify a couple of things, the two children that will be turning five and going to school, if they are in the Tempe, Gilbert, Chandler, and Mesa area there is an excellent after-school daycare program that is really cheap and really nice at the schools themselves, usually called kidzone or challengers program. However, I would agree that the youngest child’s day care can get pretty expensive. Anyway, I would suggest this, you will need to go back to court and ask for conciliation services so that you can discuss a parenting plan that will recognize you have moved out of state and making visitation modifications as such, also during this time if you can make agreement with your ex as to the return of the children and another parenting plan that will take effect after “return” date (when the children return to you) then you clearly would have something that would be more enforceable for the court because it was planned ahead and agreed upon. The downside is, if he “the ex” does not agree with what you want and you cannot work it out in conciliation services it will go before a Judge, your judge assigned to your case. I have found that a lot of the judges are extremely reluctant in moving the children. Again, another hurdle I think would be a problem for the judge is the ex has been primary care taker for a said amount of time and that would be an influential to the judge if the ex argued for them to stay.
I have seen four cases with similarities to yours and of those for 3 the children stayed and 1 the child did not, but when the father exploded in court it was an easy decision for the judge from that point forward. I did see another case which there was an agreement but it did not happen until later (like three months) and the ex was complaining that the mother had no right to take them to Va. The Judge did not buy it, but I did not know any of the details of that case.