Okay, kiddo, so feminism is like a superhero team that fights for the rights and equality of girls and women. Sometimes people think that girls and women are less important or less capable than boys and men, and that's not fair or true. But feminism says "no way!" and works to make things equal for everyone.
Now, who needs feminism? Well, imagine you're playing a game with your friends, and someone says "you can't play because you're a girl". Or imagine your sister wants to be a scientist, but someone tells her she's not smart enough because she's a girl. Those are just two examples of why girls and women need feminism - to stand up against people who think that just because they're girls, they can't do things or don't deserve the same respect and chances as boys and men. But it's not just girls and women who need feminism - boys and men benefit from it too, because feminism works to make things fair and equal for everyone. So really, everyone needs feminism!