Girls spend 40% more time performing unpaid household chores than boys, according to a new report from the UN children's agency.
Unicef said the difference in time spent working amounted to 160m extra hours a day worldwide.
Two out of three girls cook and clean in the home, and almost half collect water or firewood.
They also perform more "less visible" domestic work like childcare or looking after the elderly, the report says.
It also found that the extra workload increased with time: between ages five and nine, girls spend 30% more time on chores - by 14, it rises to 50%.
Tasks such as gathering water or firewood can also put young girls at increased risk of sexual violence, the report says.
In Somalia, girls between 10 and 14 years old spend 26 hours a week on household chores - the most of any country. Burkina Faso and Yemen also have some of the largest labour gaps between boys and girls.
"Girls sacrifice important opportunities to learn, grow and just enjoy their childhood," Unicef's Anju Malhotra said.
"This unequal distribution of labour among children also perpetuates gender stereotypes and the double burden on women and girls across generations."
The report, which also includes data on violence, child marriage, female genital mutilation and education, is being released to coincide with the UN's international day of the girl child on 11 October.