National Union of Students President Aaron Porter has backed a day of student action on Tuesday, after admitting to "dithering" over protests.
Mr Porter angered some protesters by condemning violence at an NUS-backed protest on 10 November as "despicable".
He did not back last Wednesday's UK-wide day of action, but is now calling on student unions to support protest activities on Tuesday.
Also, police urged parents to warn children of potential protest dangers.
On Monday, about 50 students staged a sit-down protest on Oxford Street.
They tied themselves together with rope, blocked the pavement and shouted slogans critical of Deputy Prime Minister Nick Clegg.
Student occupations are continuing at a number of universities, including University College London and the School of Oriental and African Studies (SOAS), in the wake of a host of protests, walkouts and sit-ins across the UK on Wednesday.
Students are angered by government plans to allow universities to charge tuition fees of up to £9,000 a year, and cuts to teaching grants and support allowances for low-income further education students.
They are particularly targeting Liberal Democrat leaders, who pledged to oppose tuition fee rises before the election but have spoken in support of the government's plan.
Deputy Prime Minister Nick Clegg, however, has declined to rule out Lib Dem ministers abstaining in the vote on the measures, expected before Christmas.
In a statement on the NUS website on Monday, Mr Porter called for a "fresh wave" of protest.
"I want to be clear and unequivocal in my support of student led, non-violent protest," Mr Porter wrote.
He said those carrying out occupations and planning protests should work through their students' union, ensure their actions are "aimed firmly and squarely at MPs" and carry out their activity "without violence or damage to property".
He also said the NUS would organise a day of action and a lobby of parliament in the run-up to the vote.
On 10 November, an estimated 50,000 students turned out for an NUS-backed march in London, which flared into violence as a smaller group occupied and damaged the Millbank building containing the Conservative Party Headquarters.
Mr Porter's strong condemnation of the violence prompted calls for his resignation from some student protesters.
He pulled out of a meeting by the Education Activist Network, a loose alliance of unions, Socialist Workers party supporters and other activists, which was one of the groups co-ordinating last week's protests.
Addressing students occupying UCL on Sunday, he said the NUS had "perhaps been too cautious and too spineless" in supporting student activism.
"I just want to apologise for my dithering over the last couple of days," he said, "I've seen sense now".
Schoolchildren younger than 16 were among those protesting last Wednesday.
Speaking ahead of Tuesday's planned protest, Metropolitan Police's Commander Bob Broadhurst asked parents to talk to their children about possible dangers at protests
"Schoolchildren have as much right as anyone else to protest, but young people are more vulnerable and likely to be injured if violence breaks out," he said.
"There is only so much police officers can do once they are in a crowd of thousands," he said.
Lib Dem protest
Also on Monday, more than 100 Liberal Democrat parliamentary candidates called on leader Nick Clegg to oppose government plans to raise tuition fees in England.
The 104 activists, who did not win seats in the last election, want all 57 Lib Dem MPs to vote against plans to allow fees of up to £9,000 a year.
They say the party's integrity is at risk and warn it could face many years "back in the political wilderness".
The government says its proposals are fair and progressive. Students will not have to repay the money the government loans them for their fees until they begin earning at least £21,000 after graduation - up from £15,000 at present.
Remaining debts will be wiped out after 30 years, raised from the current level of 25.
It argues that graduates benefit from their studies and should help foot the bill.
But critics say the government's plan to cut teaching grants by up to 80% - essentially removing state funding for many arts and humanities courses - is disproportionate.
Last Wednesday, there were 35 arrests and 17 injuries - including two to police officers - as an initially peaceful anti-fees rise protest in Whitehall flared into violence.