From Bulbapedia, the community-driven Pokémon encyclopedia.

A Picnicker (Japanese: ピクニックガール Picnic Girl) is a type of Pokémon Trainer that first debuted in the Generation I games. They are generally depicted as little girls in uniforms.

They raise a variety of Pokémon.

In the past, they have also been known as Jr. Trainers♀. In the original version, they are apparently called Girlscouts, although supposedly this had to be changed for legal reasons. Their male counterparts appear to be Campers.

Appearance

Picnicker Sprites

Image from Pokémon Red and Blue

Image from Pokémon Gold and Silver

Image from Pokémon Ruby and Sapphire

Image from Pokémon FireRed and LeafGreen

Image from Pokémon Diamond and Pearl

Generation I-introduced trainer classes
Beauty | Biker | Bird Keeper | Black Belt | Boss | Bug Catcher | Burglar | Champion | Channeler | Cooltrainer Cue Ball | Elite Four | Engineer | Fisherman | Gambler | Gentleman | Hiker | Jr. Trainer♂ | Jr. Trainer♀ | Juggler Lass | Leader | PokéManiac | Trainer | Psychic | Rival | Rocker | Rocket | Sailor | Scientist Super Nerd | Swimmer | Tamer | Youngster
Beta classes
Chief | Pokémon Prof.

Generation II-introduced trainer classes
Boarder | Camper | Firebreather | Guitarist | Kimono Girl | Medium | Mysticalman | Officer | Picnicker PokéFan | Rocket Executive | Rocket Grunt | Sage | Schoolboy | Skier | Teacher | Twins