Nana Lupita and the Magic Sopita

Luna and her little brother Sol are out to solve a mystery! They suspect that their grandmother uses magic to create her remedies because she says that she uses a "magic" ingredient. At the beginning of the story Luna and Sol catch colds so their grandmother makes a healing soup. Luna overhears Nana singing a classic Spanish children's song about frog tails while cooking the soup, so Luna secretly thinks that frogs are the magic ingredient. The children explore the enchanted garden in search of frogs until it is time to eat, in which Nana reveals the real secret ingredient. Can you guess what it is?