The speaker is a young boy, probably anywhere from 8-12 years old, judging from his "mammy" and "daddy frog" vocabulary. He's learning the biology basics in school, and takes matters into his own hands, collecting frogspawn like it's going out of style. His excitement and enthusiasm for the muddy and stinky elements of spring give off an innocent and exhilarated vibe (slapping around in mud puddles isn't exactly common practice for adults). His wide-eyed innocence makes him extra curious and he devours all the information and frogspawn experience that he can take in.
But our speaker doesn't stay googly-eyed over frog goop forever. Just like the spring season in which the poem takes place, he goes through quite the transformation. As the title suggests, his attitude toward nature, and his froggy friends, ultimately changes: "The great slime kings / Were gathered there for vengeance" (31-32). What was once a grand old time now becomes tinged with ickiness and, worse, danger. It's as if some of the blissful ignorance of youth has been replaced by a new wariness about the wider world. Our little tadpole of a speaker takes another step toward becoming a big ole bullfrog. Don't act like you don't know! Growing up is hard to do.