But why would you WANT to play a 0 level character? Or GM a 0 level party?
I don't get this.
I%u2019m a little torn about it, cuz on one hand, I can understand the desire to play characters since their early days, when they were still training for whatever profession they wished to become, a la Harry Potter, where the main characters are just kids still learning magic, with only a few weak-ass spells at their disposal. But on the other hand, level 1 characters in D&D are already pretty incompetent and pathetically weak enough as it is, and level 1 casters only know a few weak-ass spells as well%u2014even with all the hand-holding in 5e compared to earlier editions. So level 1 pretty much already IS apprentice level, which is why many groups start their characters at higher levels.
I%u2019ve only played a single level 1 session in decades, and that was only to give someone completely new to RPGs are general feel for the game and startup characters. But I generally treat level 3 as the starting level and consider it to be the default level for all %u201Cprofessionals%u201D (including NPCs) in the game world, and levels 1 and 2 to be just %u201Ctraining levels%u201D, the equivalent to level %u201C0%u201D in OD&D.
While I DO always start new campaigns at level 1, I agree with VisionStorm otherwise.
AD&D 1st Level Classes and Titles:
Cleric = Acolyte
Druid = Aspirant
Fighter = Veteran
Paladin = Galant
Ranger = Runner
Magic-User = Prestigitator
Illusionist = Prestigitator
Thief = Rogue (Apprentice)
Assassin = Bravo (Apprentice)
Monk = Novice
Other than 'Veteran' these all sound like totally green recruit names; so that seems to be the implication at least back then.
If you wanted to play children, I'd maybe do first level characters but hold back some of their attributes - or give them the 8's straight down and point buy when they 'grew up'.