After Sita had been banished from the kingdom of Ayodhya, she took refuge in the ashram of the sage Valmiki, which was located in a forest on the banks of the River Tamsa. Lav and Kush were born in this ashram. They were educated and trained in military skills under the tutelage of Valmiki.
When Rama performed the Ashvamedha Yagya, the horse strayed into their forest, which brought them into conflict with their own father. Unaware that Rama was their father, they captured the horse and refused to release it, instead engaging him in a brief conflict. When Rama found out their identity, he took them back to Ayodhya.
They grew up into just rulers like their father and founded the cities of Lahore and Kasur respectively. Lahore is now second largest city of Pakistan. The Lohana tribe, of the Kshatriya caste, claim their descendancy and aristocratic legitimacy from Lava, and have at various periods of Indian history held ruling positions in the north and west of the Indian sub-continent. Lohanas today continue to hold Lava and Rama in especially high esteem.