You actually do need to call a lawyer on this question. I am licensed in Florida. In Florida a parent cannot legally change the name of a child without the written consent of the other parent and a finding that it is in the child's best interests to change the child's name. The testimony of a psychologist or other expert is required in Florida if there is no consent. Otherwise, any one who wanted to hide a child would simply change the child's name.
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A parent has the right to apply for a name change on behalf of his or her minor child, pursuant to Minnesota Statute section 259.10, Subdivision 1. However, this is not normally granted over the objection of the other parent. The Minnesota Supreme Court has held that: ". . . judicial discretion in ordering a change of a minor's surname against the objection of one parent should be exercised with great caution and only where the evidence is clear and compelling that the substantial welfare of the child necessitates such change." (See Robinson v. Hansel, 223 N.W.2d (Minn. 1974).
That said, I wouldn't take anything for granted. If you object to the name change, you need to formally object in any legal proceeding in which the mother seeks to have your son's name changed.
She can file a petition with the Court in an attempt to have the child's name changed. You may file responsive documents to note your objection to the Court. In most cases, it is unlikely that the Court will change the child's name over the objection of a parent, though it is not certain. You should consult with (and in all likelihood hire) an attorney so you can be familiar with the court proceeding before you go and also to prepare your responsive documents properly and in a timely fashion.
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