A man named Tim Templeton tells a story about his 7-year-old self and his parents, Ted and Janice. One day, Tim is surprised when an infant wearing a business suit arrives at his house in a taxi, and Ted and Janice call him Tim's little brother. Tim is envious of the attention the day-old baby receives, not to mention suspicious when the infant acts odd around him, but his parents are oblivious.
Soon, Tim learns that the baby can talk like an adult, and he introduces himself as "The Boss". Seeing an opportunity to get rid of him, Tim decides to record a conversation between the Boss Baby and other toddlers who are at Tim's house for a meeting. A chase ensues, and the cassette tape is terminated by a passing automobile after the Boss Baby threatens to tear up Tim's favorite stuffed animal, Lam-Lam. With no evidence to support him, Tim's parents ground him for three weeks.
The Boss Baby apologizes to Tim and has him suck on a pacifier that transports them to Baby Corp., a place where infants with adult-like minds work to preserve infant love everywhere. The Boss Baby explains that he was sent to see why puppies are being loved more than infants. He has infiltrated Tim's residence because his parents work for Puppy Co., which will unleash a new puppy on a pet convention in Las Vegas. The Boss Baby stays intelligent by drinking a "Secret Baby Formula" that enables a baby to act like an adult. However, should a baby not drink it after a period of time, he or she becomes a regular baby. When they overhear Boss Baby's boss threatening to fire him for not bringing in information, which would strip him of his formula and strand him at the Templetons, he and Tim agree to work together to prevent that.
Tim's parents "un-ground" him and take them to Puppy Co. for take your child to work day. While there, they slip away and find what they think is the plans for a "Forever Puppy", but they are captured by the company's founder and CEO, Francis E. Francis. They discover that Francis used to be the head of Baby Corp. and whom Boss Baby idolizes, but was ousted when it was discovered that his lactose intolerance kept the secret formula from working properly. Francis intends to have the Forever Puppies overshadow babies by stealing Boss Baby's serum bottle and injecting the puppies with it as revenge. Tim's parents go with Francis to Las Vegas, and Francis has his brother Eugene pose as Tim and Boss Baby's babysitter to keep them from interfering.
Without a steady flow of formula to maintain his intelligence, Boss Baby starts becoming a normal baby. Despite this, he and Tim evade the "babysitter" long enough to reach the airport but are too late to intercept Tim's parents. They sneak on to another plane bound for Las Vegas. There, they stall Francis' presentation when Eugene unwittingly gives away their plan. Furious at their interference, Francis locks Tim's parents up so he can burn them with exhaust from a rocket used to launch the Forever Puppies. Tim and Boss Baby defeat Eugene and move on to save their parents but are intercepted by Francis. Tim and Boss Baby push him off a ledge, making Francis tumble into the formula. Boss Baby opens the rocket to let the puppies out so they can save Tim's parents. His return to baby state is complete while on the rocket, and begins to cry, but Tim sings to him with the family song to show his appreciation, causing him to jump off the rocket before it launches. After the rocket does launch, Tim takes Boss Baby to the formula vat and he returns to his original self. Francis then emerges from the vat, having been reverted to an obese baby and tries to attack Boss Baby, but is picked up by a redeemed Eugene and tells Tim and Boss Baby that "This time, we'll raise him right".
Boss Baby is promoted and leaves. Tim goes back to being an only child, but he and Boss Baby miss each other. After Tim writes a letter convincing him to live with him as his brother, Boss Baby returns to the Templeton family as a regular baby named Theodore Lindsey "Ted" Templeton. In the present, an adult Tim finishes telling his daughter the story about how he felt when his brother was born, to calm her worries about her recently-born sister, whom she notices that her sister is also another Boss Baby like Ted was.
I like that movie