A Florida school bus carrying dozens of students crashed and careened into a lake -- and everyone made it out uninjured thanks in part due to a 10-year-old boy.The bus took down a signpost and part of a tree before flipping on its side in the water on Thursday in Hillsborough County, located outside of Tampa, authorities said.Parents and first responders rushed to the scene and that's when Nicholas Sierra, 10, witnessed the driver struggling to bring the bus to a stop."I saw him stepping on the brakes, but the brakes weren't working and then everyone started screaming," Sierra said.As the bus crashed Sierra sprang into action, helping children off of the bus."I grabbed a kindergartener's arms and put her around my neck and brought her to land, and then I went back," he said.Witnesses also called the bus driver a hero, saying the man stayed on the bus until every child got out safely.Investigators are working to determine the cause of the crash, but the driver has said he believes the brakes failed.