The new pill is a combination of three drugs used to treat tuberculosis, mixed in the right dosage, and is fruit-flavoured to appeal to children.
Until now, the global TB Alliance says pills designed for adults have been split to get the dosage for children.
Every year, about a million children fall ill with TB, which is the world's deadliest infectious disease.
In 2014, an estimated 140,000 children died of TB, according to global figures from the World Health Organization (WHO).
Kenya is the first country to roll out the new drug nationally, with more countries expected to follow over the next three years.
Experts say the new treatment will be more effective because the components have been measured accurately and the pill is not bitter-tasting.