you say wife? so i assume - no divorce or custody order in place.
since no custody order exists, what she did is not legally wrong. morally, maybe. but she was within her rights.
but at this time, you have the same rights. no one has specific custody of the children. you could go and get the children at anytime. the only one who could refuse you would be the mother. (let me also state, this may not be a good idea - it could lead to police involvement and charges being filed against you by the mother-in-law or your wife, for tresspassing, peace disturbance, assault, ets.... see where I am going with that one?)
now, if you are sure that this is headed to divorce and no way to work it out. i would suggest filing it. if you do, florida will hold the jurisdiction for the child. your wife can not file for divorce or custody until she mets the residency requirements of the state (usually 6 months). by you filing early, it will require her to travel back to florida for the hearings and will keep florida as the jurisdiction for the child.)
now when you go to court, be sure that the fact that she plans to relocate is known to the judge. that way, it will reflect in the visitation schedule and also the decision on custody.
to be honest, the fact that she went home to her family will be of help to her on the relocating. your marriage is ending and she is going back for physical and emotional support of her family. if she were just moving off to anywhere with no friends or family - it would look worse.
the biggest suggestion, if you still love her and there is a chance to work things out. DO IT!!!! If there isn't, start covering your bases now.