Zimbabwe has more orphans per head of population than anywhere else
Some governments around the world are putting politics before the lives of Zimbabwe's children, British charity Save the Children UK told the BBC.
It says they are withholding funding until there is true political reform.
There are an estimated 1.5 million orphans in Zimbabwe, the highest number per head of population in the world.
A charity official suggested fears that aid would be misused by President Robert Mugabe were unfounded as it could be channelled through the UN.
The BBC's Mike Thompson, who has just returned from Zimbabwe, says that some estimates put the total number of orphans in the country as high as 1.8 million.
Most have lost their parents through HIV/Aids, malaria or cholera.
Yet many nations are reluctant to offer more financial help, he says, in case it is misused by Mr Mugabe, the man seen as the architect of the country's problems.
But Save the Children UK's country director in Zimbabwe insists it is short-sighted of some world leaders to continue denying children much needed help, which could be given through aid agencies.
Meanwhile, UK Minister for Africa Mark Malloch Brown says Britain wants to renew its ties with Zimbabwe.
He said the power-sharing deal between President Mugabe and the Prime Minister, Morgan Tsvangirai, who leads the former opposition Movement for Democratic Change, was working better than expected, although the MDC was still in a very difficult position.
"They [the MDC] clearly do not have any say over the security apparatus or over issues of political freedom and predictably President Mugabe is keeping a tight grip on his presidential powers and privileges so it's a mixed picture," he told the BBC's World Today programme.
Mr Malloch Brown, who is in Mozambique as part of a tour of southern Africa, said any steps towards re-engagement would be stopped if the political situation deteriorated in Zimbabwe.
"We are willing to take this inclusive government, if you like, on probation and try to support it but if indeed we see a rash of new attacks on opposition leaders or people being imprisoned unjustly then that process of re-engagement would reverse itself.
"But for now all of those who are supporting change in Zimbabwe, the progressive leaders in the region, others outside, I think want to make the same wager, to take a careful gamble on the good guys prevailing."