The global body's expert group - known as SAGE - said that while more data on children between 6 months and 10 years are needed, countries that have made vaccinating children a priority can also administer them a single dose in order to ensure that as many as possible are immunized quickly.
"The SAGE recommendation (for children under 10) could change as more data come in," said WHO vaccine chief Marie-Paule Kieny.
For the time being, she said, "the priority should be to give them at least one dose of vaccine now, and to cover as many of them as possible."
The expert group, which held a three-day meeting in Geneva this week, said medical regulators should have the final say on which vaccines can be administered as a single shot.
But its recommendation is an important indication for those regulators - particularly in the developing world - that haven't yet decided how many doses should be required.
U.S. regulators have recommend two doses for children under 10.
Europe's drug authority EMEA last week said the swine flu vaccines it has licensed should be given in two doses, at least three weeks apart, to all age groups. EMEA noted that current data were too "limited" to allow the agency to recommend one dose.
Swine flu has killed at least 5,700 people worldwide since the A(H1N1) strain appeared in April, according to WHO's tally.
Governments in the northern hemisphere are under pressure to carry out their vaccination campaigns before the winter flu season starts. The number of doses authorities recommend will play a decisive role in determining how far available vaccine stocks will stretch.
The experts also recommended to WHO that pregnant women use those licensed vaccines deemed safe by regulators. The recommendation is based on the high risk that swine flu poses to pregnant women, as well as on animal tests showing vaccines are safe for mother and child.
Seasonal and pandemic flu vaccines can be given simultaneously, provided at least one uses "inactivated" virus, which isn't contagious anymore, the experts said.
AP medical writer Maria Cheng in London contributed to this report.