Alright kiddo, let me explain what russification of Ukraine means.
Do you remember when we learned about how different countries have different languages, cultures and traditions? Well, Ukraine is a country that has its own language, culture and traditions. But a long time ago, another country called Russia, which is next to Ukraine, wanted Ukraine to be more like them. They tried to make Ukraine speak Russian, follow their customs and be more like them. This is what we call russification of Ukraine.
It's like if you and your friends love to play with dolls and draw pictures, but another friend comes along and tries to make you play with cars instead. You might not like it because you have your own way of having fun.
Many Ukrainians didn't like being told to be more like Russia and they still want to keep their own culture and language. This caused some problems between Ukraine and Russia, like arguments and disagreements. But people are hoping that one day they will be able to be friends and respect each other's differences.