The series follows two teenagers, Teddy and PJ Duncan and their 10-year-old brother, Gabe whose parents enlist their help when they return to work after the birth of their fourth child, Charlotte (nicknamed "Charlie"). With their parents juggling full time careers, they pitch in, getting very familiar with baby formula, burps, clothes, and babysitting while navigating typical teenage life. In each episode, Teddy creates a personalized video diary for Charlie. Each video will chronicle Teddy's daily adventures and mishaps for Charlie to use as advice when her big sister is no longer living at home.