If there is no court order in effect, than she can take the children out-of-state. However, her husband can go to court and obtain an order which will require her to remain in the state (or return if she leaves beforehand). If at that point she leaves (or fails to return), she can be charged with parental kidnapping.
The safest and best way for her to obtain legal custody of the children is for her to go to court first. What she wants to do is get a temporary order from the court on custody and visitation. It will be temporary because a final decree will be issued upon divorce. The court will consider the bests interests of the children in making its determination. The court will look at the age of your child, the relationship of the parents and the child, the present living situation of the child, etc. Address the issue of an out-of-state move at that time.
Note: She could file for custody once she re-establishes residency in her new state but that will take time. In the meantime, her husband could file. And as stated above, she would then need to to return to KS.
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