The tale of the Frog Prince is best known for the version by the Brothers Grimm (academic linguists who studied folklore and retold the tales as was fit for the time).
The gist of the story is a princess who meets a frog at a pond, who eventually kisses him and he turns into a handsome prince.
Most folk tales have traces of ancient magic in them in one form or another. The frog was symbolic of fertility & birth, because of the breeding times of frogs in the ponds and the rains that came at the turn of season.
The frog was symbolically used by the wise women as a love spell to promote fertility.
"Do not be afraid of me my fair lady."