Tiny bipolar humans under the age of 3, who can swing rapidly between endearingly cute antics and screaming, kicking, biting fits of rage. Completely unpredictable and often unintelligible lovable little walking blessings/nightmares disguised as tiny human beings with giant heads. Prone to selective hearing and repeating overheard curse words at inopportune moments. More dangerous when traveling in packs. Evolutionarily speaking, it is ridiculous that humans have the ability to reproduce fast enough to be the parent of more than one toddler at a time.