When Rishi Agastya cursed both Suketu and Sumali to death, Thataka took it upon to herself (with her son, Subahu's, aid) to wreck vengeance on the sage. This earned them both the Rishi's anger. Agastya cursed Thataka with the loss of her beautiful physique, and transformed both mother and son into hideous demonic creatures with a cruel, cannibalistic nature.
As revenge, Thataka and Subahu attempted to harass as many rishis as they could, by destroying their Yagnas with rains of flesh and blood. Brahmarishi Vishwamitra was especially at the receiving end of Thataka's harassment. Unable to cope with her mischief any longer, Vishwamitra finally approached Dasaratha, the King of Kosala, for help. The King obliged by sending two of his four sons, the 16-yr-olds, Rama and Lakshmana, to the forest, charging them to protect both Vishwamitra and his Yagna
When Thataka and Subahu both attempted to destroy yet another of Vishwamitra's yagnas, Rama warned them not do so. They responded by laughing at Rama, and deriding him as a 'mere boy'. The 'mere boy' retaliated by slaying both mother and son swiftly.
This act gained the young princes the blessings of not just Vishwamitra but also the blessings of all of the assembled sages in the yagnashala