Okay, so imagine you're in a group with your friends and you all love the same thing, let's say it's playing with Legos. You all have different kinds of Legos and you all build different things with them, but you love Legos so much that you decide to make a club just for people who love Legos like you do.
Now imagine that there are other groups of people who love different things, like playing with dolls or playing soccer. Each group has their own club and they all have different ideas about what they like best. But sometimes, the groups argue with each other about who is the best and who should have the most toys to play with.
Belgian nationalism is kind of like that, but instead of Legos or dolls, it's about people who live in Belgium and what they think should be important for their country. Some people in Belgium feel really proud to be from their country and they want everyone to work together to make it the best it can be. They think it's important to have a shared language, culture, and history that everyone can be proud of. They are called Belgian nationalists because they believe that everyone should work together to make Belgium a great place.
But other people in Belgium don't think that way. They might feel really proud of the region they come from, like Flanders or Wallonia, and they might feel like their own culture and language is more important than anything else. They think that each region should have more control over their own part of the country and that it's okay to have different things that they like best. They might even think that their own region should be its own country instead of being part of Belgium at all.
So just like the different groups of people who love different things, there are different groups of people in Belgium who have different ideas about what's important for their country. Some want everyone to work together and be proud of Belgium as a whole, while others want more independence for their own region. It's kind of like a big family where everyone has different ideas about what they want for dinner, but they all still love each other and want to find a way to make things work.