"Bolsonaro Jr." often refers to Flávio Bolsonaro (born 1981), the eldest son of Jair Bolsonaro, but it can also refer to one of his other sons, including:
None of Jair Bolsonaro's children (including his daughter Laura, born 2010) has "Junior" or "Júnior" in their full name.
The moniker is used mainly by politicians in other countries (notably, Donald Trump) and on occasion by global news outlets.