Okay kiddo, imagine you have two friends, one who loves chocolate and the other who loves vanilla. Now imagine you want to make a cake to make both of them happy, but you don't know the right recipe. You try adding some chocolate and some vanilla to the batter, but your friends still aren't happy.
Mixed anomaly is like that. It happens when two different things in nature, like particles or forces, have their own rules that don't work together. Scientists try to find a "recipe" that can make both of these things happy, but sometimes it's really hard. This can happen in physics, which is the study of how things work in the universe.
Just like how you need to find the right mix of chocolate and vanilla to make your friends happy, scientists have to find the right mix of rules to make particles and forces happy. It's tricky, but they keep trying until they figure it out!