LEON, Mexico -

Pope Benedict XVI worked to build the future of Mexico's church by reaching out to children Saturday as tens of thousands of teenagers streamed into a vast, shade-starved park to camp out overnight ahead of a gigantic papal Mass.

Benedict awoke to the pre-dawn serenade of two dozen youths from a Guadalajara church group who sang him a traditional folk song after getting as close as security would allow to the college in Leon where the pontiff is staying during his three-day visit to Mexico.

"We sang with all our heart and all our force," said Maria Fernanda de Luna, a member of the group. "It gave us goose bumps to sing 'Las Mananitas' for him."

Benedict has taken up Pope John Paul II's drive to reach out to young Roman Catholics, following in his footsteps by rallying millions of young faithful to join him for World Youth Days, the Catholic youth festivals held once every three years. The next edition is scheduled for Rio de Janeiro next year.

His only public remarks Saturday were planned for a meeting with about 4,000 children in Peace Plaza in the city of Guanajuato, a space that was crowded with cheering and flag-waving well-wishers long before he arrived.

At the entrance to Guanajuato, he received the keys of the city and then traveled by popemobile past faithful crowded along cobblestone streets of the historic colonial city, birthplace of Mexican independence and an armed uprising against harsh anti-clerical laws in the 1920s. He was expected to refer again to the need for them to stay away from the drug-fueled violence that wracks Mexico.

As he left his residence late Saturday afternoon to meet with President Felipe Calderon in Guanajuato, Benedict went out of his way to bless dozens of babies handed up to him by their parents. While such gestures are routine papal fare, Benedict seemed to zero in on the children in the crowd.

"We young people are getting closer to the church and to God, instead of getting closer to drugs and violence," said Juan Daniel Pacheco, 18, of Apaseo el Grande in Guanajuato state as he sought shade with his friends at one of the campgrounds that were quickly filling with faithful arriving for Sunday's Mass. "We are young people who will be able to change Mexico."

The focus on youth fits with the Vatican's drive to re-evangelize parts of the world where Catholicism has fallen by the wayside, trying to rally the next generation to embrace a faith that their parents may have abandoned. While Europe has certainly been Benedict's focus to date, Mexico also has seen its number of Catholics fall.

"The Mexican church feels like it's lost a few generations of Catholics," said Joseph Palacios, a professor of Latin American studies at Georgetown University, citing the battles over liberation theology that drove many left-leaning Catholics away. To get back its numbers, the Mexican church is "moving forward with the new generation," he said.

Yet as much as Benedict was receiving a rapturous welcome from young Catholics, his first full day in Mexico was not without criticism -- particularly concerning the church's treatment of children and sexual abuse.

On the second day of the pope's visit, victims of Marcial Maciel launched a new book containing documents on the Vatican's alleged cover-up of sexual abuse of seminarians by Maciel, the founder of the Legionaries of Christ.

Alberto Athie, former priest and one of three co-authors of "The Desire Not to Know," called on Benedict to publicly recognize the church's responsibility for Maciel's abuse.

"The church won't fall. On the contrary, it will be reconstructed," he said.

Of the 43.5 million Mexicans under age 20, 36.2 million are Catholic, or 83.2 percent, just under the national average. The largest group of Mexicans overall are children aged 5 to 9 -- a prime target for Benedict's efforts to rebuild a church that has fallen victim to the same secular trends that have emptied churches across Europe.

Benedict will greet tens of thousands more on Sunday, when he celebrates Mass in the enormous Bicentennial Park.

Despite the heat, a festival atmosphere prevailed as thousands of Mexican teens streamed out of buses from across the country to set up camp at the park, many singing or playing guitars to the tune of the song "La Bamba," with the lyrics slightly changed: "Para ver al Papa, se necesita una poca de gracia." ("To see the pope, you need some grace")

The weeklong trip to Mexico and Cuba is Benedict's first to both countries, and only his second to Latin America. He visited Brazil in 2007.

Many said the pope's message of peace and unity would help heal their country, traumatized by the deaths of more than 47,000 people in a drug war that has escalated during a government offensive against cartels that began at the end of 2006.

Teens on Saturday said the damage of violence and drug use emphasized the importance of staying on a religious path.

"I've been drawn closer to all that is spiritual because it helps me in life," said Carla Patricia Maldonado Moreno, 15, of nearby Celaya. "I know I'm not going to surrender to whatever obstacle."

Pilgrims streamed in from all over Mexico and as far away as Phoenix, Arizona.

Paula Zazueta traveled 40 hours by bus from Phoenix with 43 people, who first went to Mexico City to see the shrine of the Virgin of Guadalupe and later to the camp in Silao to await the Mass.

"The blessings he will give us are important," said Zazueta, who owns a video production company.

"It is faith that moves us," said Alejandra Angoa, 34, a handicrafts-maker from the state of Tlaxcala. She walked alongside people of all ages carrying sleeping bags, coolers, backpacks, rolling suitcases and jugs of water to the campsite in 86-degree (30 degree centigrade) weather.

Marcela Perez, 35, was exhausted after the trek and huddled in the only shade she could find alongside a portable toilet. But she did not regret coming.

"I think it's worth it," she said. "He is the head, the rock for us who have been baptized, for the church. It's a unique experience."