From the Super Mario Wiki
Piranha Sprouts (Chuchu Pakkun in Japan) are Piranha Plants who appear in Yoshi's Story, and only appearing in Stage 4-3: Piranha Grove.
Piranha Sprouts are one of the few variations that have the ability to walk. They are found in the game Yoshi's Story. They look like the bud of a Piranha Plant with green shoes (or leaves resembling shoes). Their ability to walk is extremely limited to short waddles. Piranha Sprouts, like Pests, are able to shrink anything that escapes from their mouth. It makes an odd squeaking sound. The only known way of defeating a Piranha Sprout is by shooting it with an egg.
Piranha Pests are an exotic variation of Piranha Plant indigenous to Piranha Grove.