Okay kiddo, so you know how we have different ways of keeping track of time? We have seconds, minutes, hours, days, weeks, months, and years. These are all units of time that help us measure how long something takes.
The smallest unit of time is a second. It's very short, like when you count "one Mississippi." A minute is made up of sixty seconds, so it's longer than just one Mississippi. An hour is made up of sixty minutes, so it's even longer.
A day is made up of 24 hours. We usually use days to talk about how long something takes, like how long it takes for the earth to rotate once on its axis. We also use weeks, which are seven days long, to talk about schedules, like when you have school.
Months are a way we measure time based on the moon's cycle. The moon takes about 29.5 days to go around the earth, so months are about that long. We use months to talk about things like when your birthday is or when holidays happen.
Years are longer than months. A year is made up of 365 days or 366 days (in a leap year), and we use years to talk about how long ago things happened, like when your grandparents were born.
So there you have it, sweetie! A unit of time is just a way to measure how long something takes, and we have lots of different units to choose from depending on how much time we need to measure.