"Under-five" means kids who are younger than 5 years old. You might hear people talk about under-five kids when they're talking about things like healthcare, education or nutrition. It's a really important stage of life because when you're under five, you're still growing and developing really quickly. Your brain is still learning lots of things, and your body is getting stronger too.
Sometimes, kids who are under-five need extra help to grow up strong and healthy. That's where things like vaccinations, good food, safe water, and healthcare come in. When you're under-five, it's also really important to be safe and avoid things that might make you sick or hurt you. That's why adults take extra care to keep under-five kids safe and healthy.