Vampyre Juveniles are the lowest rank of vampyres. The ones in the Burgh de Rott Woods can be damaged with any weapon, and the ones in Meiyerditch require a Silver or Blisterwood weapon to damage, making them similar to a juvinate. They differ in capitalization, the Burgh de Rott ones having an upper case J. If you use a Guthix balance potion on them, one of three things can occur, they can be killed instantly, turned into an Angry vampyre, or turned back into a human, and give the player a small reward.
If a Guthix balance potion is not used on the ones in Meiyerditch, then the Juvenile will say "Ha ha, time to disappear and re-rejuvenate!", turn into a cloud of mist and float away when it reaches approximately 0 health. No drops will be received when this happens.
Vampyre Juveniles and Vampyre juveniles used to be significantly different, the latter having a much older, albeit unique, model, despite being released later. The graphical updates to Morytania and vampyres solved this, making the two look the same. The combat levels and capitalisation remained different though.