WATCH: Biden's Education Secretary says children missing from urban classrooms simply moved during pandemic

On Sunday's episode of "Face the Nation," host Margaret Brennan asked Biden Education Secretary Miguel Cardona where all the children who were once enrolled in big cities had gone, as data shows they haven't returned to school post-pandemic. Brennan asked, "How widespread is this problem of having lost children in American school systems?"

To which Cardona replied, "in particular urban centers, where we know the pandemic impacted, urban centers where the density is higher, many families moved out of cities."

Brennan cited a statistic she received from the superintendent of the Los Angeles School District who told her 10 to 20,000 children are simply missing from the school system.

Brennan brought up many issues facing American schools, such as the problem of teacher shortages, to which Cardona suggested using money from the American Rescue Plan to bring retired teachers back into schools, and to start student teachers on the job earlier.

Brennan questioned how the Biden administration would be able to encourage states to use their allotted funds in the way that the DOE would like, but for Cardona, a bigger problem is that there's a "teacher respect issue."

Cardona suggested that teachers need to be paid more, and have "better working conditions so they can continue to grow." He suggested that "teacher voices" need to be brought in to "re-imagine schools."

As to why teachers may have left the profession during the pandemic, Cardona said that they left because people just didn't have enough respect for those teachers. They didn't have the working conditions, he said "to feel connected to the community." For Cardona, the big problem is that teachers don't feel supported or get enough respect.

New York has experienced a similar scenario of losing students, as student enrollment has dropped 9.5 percent since the start of the Covid pandemic. Roughly 30,000 fewer students are expected to enroll in 2022 compared to 2022.

Since the start of Covid, 1.27 million children simply stopped attending public schools, or about a 2 percent drop, with most of those absences found in Democrat run cities according to ReturnTo Learn.

Researchers at Stanford University found a primary cause for the drop in public school attendance: the decline of in-person learning.

Throughout the Covid pandemic, public school teachers, with their unions leading the way, promoted remote learning for as long as possible, with many educators saying they still prefer the method.

A Professor in Stanford’s Graduate School of Education, Thomas Dee, said "Parents demonstrated they didn’t want kids at that age sitting in front of a computer."

Further, as Cardona noted, many families are moving out of cities altogether.

A study by the Institute of Governmental Studies at the University of California Berkeley found that the downtown and urban centers of major US, Democrat led cities have seen activity drop by nearly 50 percent as people have moved away.

People are leaving cities like New York and Los Angeles in droves due to historic high crime and homelessness.

In July information released by the real estate firm Redfin showed homeowners want to flee Democrat led cities and move to safer, more affordable locations, most of which are in Republican led cities and states, such as Florida.