Neighborhood watch is like when all the mommies and daddies in a block help to keep each other safe. They all work together to watch out for any bad things happening in their community. Just like you watch out for your little brother when your mommy is busy, the people in the neighborhood watch out for each other's safety.
They keep an eye on anything or anyone that seems strange, like if there is someone who doesn't live in the neighborhood and looks like they are doing something bad or if they notice someone breaking into somebody else's house. They report these things to the police and try to stop anything bad from happening.
They also help make sure that everyone in the neighborhood is safe by reminding each other to lock their doors, close their windows, and not to leave their toys outside. They help to keep their community clean and protect it from any danger.
In short, it's like a big team of friends and family who all take care of each other and their community.