Instant Teen: Just Add Nuts(2000)

Otona Ni Nuts

Natsumi Kawashima, an energetic fifth-grader, is obsessed with her fantasy of being the ideal, sexy woman. Rejected at every advance by the cute guys that she fawns over, she finally gets a break when she picks up a package of mysterious pink nuts that are adults only.

Eating these nuts causes her to morph into a voluptuous adult, and she's offered modeling opportunities and suddenly becomes noticed by guys who wouldn't have given her the time of day before.

But, she's still a kid inside and is about to learn that things don't always work out exactly as you hope they will...

(Source: Tokyopop)

Included one-shot:
Volume 1: Fortune★Cookie
Volume 2: Sakuranbo☆Kiss (Cherry☆Kiss)