1. How to measure the height of a 3-year-old baby. What should you pay attention to when measuring the height of a 3-year-old baby? This section will introduce the correct measurement methods, as well as common misunderstandings and solutions. First, you need to choose a flat ground as the measurement location and make sure your baby\’s feet are bare. Then, use the corner or door frame as a reference to have your baby stand up straight and close to the wall.