Simplify the following text for a Grade 5 native English-speaking person.
Original: Powder monkeys were boys or young teenagers who used to work on board the old sailing ships when they went to war . When there was a battle it was the powder monkeys ' job to carry bags of gunpowder from the place where it was stored to the people who were operating the guns .
Simplified: Often , powder monkeys were boys or young teens selected for the job for their speed .