SAN ANTONIO — In a crushing blow to the state’s huge seizure of children from a polygamist sect’s ranch, the Texas Supreme Court ruled yesterday that child welfare officials overstepped their authority and the children should go back to their parents.

The high court affirmed a decision by an appellate court last week, saying Child Protective Services failed to show an immediate danger to the more than 400 children swept up from the Yearning for Zion Ranch nearly two months ago.

“On the record before us, removal of the children was not warranted,” the justices said in their ruling issued in Austin.

The high court let stand the appellate court’s order that Texas District Judge Barbara Walther return the children from foster care to their parents. It’s not clear how soon that may happen, but the appellate court ordered her to do it within a reasonable time period.

The ruling shatters one of the largest child-custody cases in American history. State officials said the removals were necessary to end a cycle of sexual abuse at the ranch in which teenage girls were forced to marry and have sex with older men, but parents denied any abuse and said they were being persecuted for their religious beliefs.

Every child at the ranch in the west Texas town of Eldorado was removed; half were 5 or younger.

“The moms are clearly very happy at the news that it looks like they’re going to get their kids a lot sooner than expected,” a spokeswoman for legal aid attorneys representing 38 mothers who filed the complaint that prompted the ruling, Cynthia Martinez, said. “It’s definitely an emotional day.”

The case before the court technically only applies to the 124 children of those mothers, but it significantly affects nearly all the children since they were removed under identical circumstances.

The Third Court of Appeals in Austin ruled last week that the state failed to show that any more than five of the teenage girls were being sexually abused, and had offered no evidence of sexual or physical abuse against the other children.

The ranch is run by the Fundamentalist Church of Jesus Christ of Latter Day Saints, which teaches that polygamy brings glorification in heaven. It is a breakaway sect of the Mormon church, which renounced polygamy more than a century ago.

Roughly 430 children from the ranch are in foster care after two births, numerous reclassifications of adult women initially held as minors, and a handful of agreements allowing parents to keep custody while the Supreme Court considered the case.

Texas officials claimed at one point that there were 31 teenage girls at the ranch who were pregnant or had been pregnant, but later conceded that about half of those mothers, if not more, were adults. One was 27.