There are missings facts here. School districts would not let her register them each year without a custody and/or guardianship order. Also she could not get their social security checks. You will need to go in person and consult with a local family law attorney.
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Forget the police. If there is no court order granting the aunt guardianship. go get your children. Your issues has little if anything to do with the school district in which they are enrolled. You really need to seek legal advice ASAP.
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