The Child Development Index (CDI) is a way for people to figure out how well kids are growing up in different places all around the world. The CDI looks at a lot of different things that can affect how well kids do as they grow up, like how much they eat, how much they get to learn, whether they have good healthcare, and so on.
It's like a special tool that helps grown-ups know how to make sure that kids are getting all the things they need to have the best chance at growing up healthy, happy, and able to do all the things they want to do.
The CDI helps people see which kids are doing well and which kids are struggling so that they can figure out ways to help them. When the grown-ups know which kids need their help the most, they can work together to make sure they get the food, education, healthcare, and everything else they need to grow up strong and healthy.