A mother was left reeling after two of her children -- including her nine-year-old daughter -- were reportedly held for 30 hours by Customs and Border Protection officers, despite being passport-carrying U.S. citizens, after trying to cross into California from Mexico to attend school.

Thelma Galaxia said she and a friend were each driving their two children from their homes in Tijuana across the border to the children's schools in San Ysidro on Monday. When they reached the Port of Entry, traffic was backed up significantly and Galaxia was worried about the children getting to school on time, so she told 9-year-old Julia and 14-year-old Oscar to walk through the Port of Entry on foot and she would order them an Uber to get to class

When the children attempted to walk across the border, however, Julia and Oscar were stopped by CBP and subsequently detained and separated from each other for 32 hours.

CBP has defended their actions in a statement to Fox News, saying their intent was to "perform due diligence in confirming her identity and citizenship."

Julia gave the officers her U.S. passport card, but said that they told her she didn't look like the girl in the photo, and accused her of being her cousin Melanie. She also said they accused her brother of sex and human trafficking, and said he would face charges if he didn't sign a document saying that Julia was her cousin Melanie.

“I was scared," Julia told NBC 7. "I was sad because I didn't have my mom or my brother. I was completely by myself."

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CBP could not clarify why it took more than a day to identify Julia as a U.S. citizen but said that the girl gave "inconsistent information during her inspection."

They added that Oscar was identified as a citizen later in the day on Monday and released, but it wasn't until about 6:30 p.m. that Julia was allowed to reunite with her family.

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Local news was present as Thelma Galaxia was reunited with her children. In the hours since her children were detained, she had reportedly called the Mexican consulate in an attempt to get them back.

According to a 2017 NPR article, at least 25,000 people cross the border between Tijuana and San Ysidro on foot every day. Many of those are students, born in the United States but living in Mexico for various reasons. As U.S. citizens, they have a right to a U.S. education, although their families could technically be fined for not attending a school in their district.

San Ysidro reportedly has the highest rate of homelessness in the country, as the price of living has risen to a staggering rate, which has driven many families across the border to find affordable housing. In some instances, a family member or parent will be deported, so children will accompany them back to Mexico but make the exhausting trip back to the U.S. daily for school.

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CBP has maintained that they prioritize the "safety of the minors we encounter" and that it is critical to "positively confirm the identity of a child traveling without a parent or legal guardian."