Childs had an immediate impact with the Cougars as a true freshman during the 2016-17 season. He played in 33 of the team's 34 games, starting in 26 of those games. He averaged nearly 26 minutes per game, scoring 9.3 points per game and getting 8.2 rebounds per game. He was selected to the All-West Coast Conference Freshman Team alongside teammate T. J. Haws.
Sophomore year
During the 2017-18 season, in his second year with BYU, Childs' numbers improved dramatically. His points per game increased to 17.8 and his free throw and 3-point percentages increased to.643 and.313, respectively. Childs was selected in January 2018 as a WCC Player of the Week. At the close of the season, he and teammate Elijah Bryant were named to the All-West Coast Conference First Team.
Junior year
Prior to the start of the 2018-19 season, Childs decided to enter his name in the NBA draft pool. While he did not hire an agent, in order to possibly return to BYU for another year, many believed that he would not return to play for BYU for his junior season. After receiving what Childs called "valuable feedback," he did decide to play at BYU for his junior year. Childs was named to the Karl Malone Power Forward of the Year award preseason watch list and was later named as one of the 10 finalists. During the year, his name was included on the Lute Olson Player of the Year and the Lou Henson Mid-Major Player of the Year awards. In December and again in January, Childs was named a WCC Player of the Week. Childs finished the year first in the WCC in scoring at 21.2 points per game and first in rebounding at 9.7 per game.
Senior year
After the close of his junior year, Childs again decided to enter his name into the NBA draft pool, this time hiring an agent. He unexpectedly decided to return to BYU for his final season saying, "I'm coming back for my senior year. Let’s make some magic happen." For the second straight season, Childs was named to the watch lists for the preseason Karl Malone Power Forward of the Year Award as well as the Lou Henson Mid-Major Player of the Year Award. He was also listed as a preseason candidate for the Naismith Trophy, the Wooden Award and the Julius Erving Award. Due to paperwork errors as part of the NBA draft exploration process, Childs did not participate in the first 9 games of the season. On February 22, 2020, Childs scored 28 points and had 10 rebounds in a 91-78 upset of second-ranked Gonzaga. On February 29, 2020, Childs scored 38 points and grabbed 14 rebounds in a win over Pepperdine. This put him over 2,000 points for his career and made him the first player in school history to score 2,000 points and collect 1,000 rebounds. At the conclusion of the regular season, Childs was named to the First Team All-West Coast Conference.
