Yes, if a child is adopted by the applicant, he can be included as a minor dependent on the application. Just being a legal guardian will not itself entitle him to be included.
How can I include my nieces and nephews as dependents in the Maltese citizenship application?
My wife and I recently became the legal guardians of our 10-year-old nephew after his parents passed away. We were considering applying for the Maltese citizenship program. How can we include him as a dependent? If we were to formally adopt him, would that be a benefit with regard to our application?
The only way to include your nephew in your application is to adopt him, as adopted children are eligible for participation in the Maltese citizenship program.
Adopted children qualify as dependents in terms of the program.