What is this insect from Brasil?
This is, indeed, a nymph (what you called a young stage), but not from a cicada as you suspected: it's a nymph from a leafhopper, which are hemipterans from the Family Cicadellidae (cicadas are also hemipterans, but they belong to the Family Cicadidae). More specifically, this seems to be a sharpshooter, which are leafhoppers from the Tribe Proconiini.

Narrowing down to the Genus is more complicated, but I'd guess it is Oncometopia. Here is an image of Oncometopia orbona for comparison:



This other image (also Oncometopia orbona) is even more similar to yours: