Okay, kiddo, so do you know what Wikipedia is? It's a website where people can write and read information about all sorts of things. Well, Wikimedia projects are a bunch of other websites that are built by the same people who made Wikipedia.
So, imagine that you have a big bookshelf with a lot of different books on it. Each of these books is like a different Wikimedia project. Some of the books might be about pictures, some might be about music or videos, and some might be dictionaries or encyclopedias.
Each book has its own special subject, and people can read them or add to them if they want. Just like how people write articles on Wikipedia, they can add pictures or sounds to the Wikimedia projects that are all part of the same big bookshelf.
Some of the other Wikimedia projects include Wiktionary, which is a dictionary with lots of words and meanings, or Wikisource, which is like a library of old books and documents. Basically, the people who made Wikipedia wanted to make sure there were lots of places where people could share information and learn new things!