In a speech launching a new child protection law, Zuma said that hosting an event of such magnitude could be seen as an opportunity for criminals, particularly during an extended school holiday.
South African schools will be closed for the month-long Cup, which starts on June 11.
"Not all parents and care-givers will be able to align their vacation with that of the extended school vacation. We urge parents to take extra care and ensure that their children are supervised and provided with guidance at all times," he said.
"Children wandering alone in shopping malls and football stadiums will be vulnerable to people with evil intentions." The United Nations says trafficking generates billions of dollars annually, with 79 percent of those affected falling victim to sexual exploitation. An estimated 6,000 to 8,000 people are trafficked a year, half of them children.
South Africa fast-tracked a new law against human trafficking to bring it into effect before the World Cup, making it easier to prosecute suspects and giving South African courts jurisdiction over acts outside the country's borders.
Those found guilty could now face life imprisonment or a heavy fine.
SECURITY BUDGET
Trafficking has not traditionally been a major issue in South Africa but activists say the problem is growing and child groups have warned of an increase in incidents during the tournament, when some 350,000 foreigners are expected to travel to the country.
Zuma said human trafficking had been prioritised within the justice system and that dedicated police co-ordinators and task teams had been set up.
"We will play our part as government but parents and care-givers also have to be vigilant," he said.
South Africa's government has vowed to keep fans safe during the World Cup, setting aside an additional 1.3 billion rand ($164.2 million) for security.
The country has some of the highest violent crime levels in the world, with more than 18,000 people murdered in the 12 months to March 2009 - around 50 a day and more than the United States which has six times the population.
Local news agency SAPA reported that Zuma had appealed to South Africans to "be good" for the month of the tournament.
"In this time, we need good South Africans. Let them, just for four weeks, be good. Just for four weeks," he said at a prayer meeting on Thursday.
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