What is "upapandavas"

In the Hindu epic Mahabharata, the Upapandavas(उपपाण्डव, lit. junior Pandavas), also known as Pandavaputras(पाण्डवपुत्र, lit. sons of Pandavas) or Panchakumaras(पञ्चकुमार, lit. five sons) are the five sons born to Draupadi from each of the five Pandavas. They are Prativindhya, Shatanika, Sutasoma, Shrutasena and Shrutakarma. They fought the battle on the side of the Pandavas, but not much is said in the Mahabharata about the brothers except for fleeting mentions during the battle. However all five of them were killed by Ashwathama on the night of the last day of the war.