In theory, Prussia should wait until he at least knew the kid's name before declaring himself the big brother... but, well, he's always been one to do things before thinking about them.

"Ja! I'll be your big brother and take care of you and make sure you grow up properly!" he makes a peace sign.

"Prussian is a person from my house! I'm Prussia so all that come from my house are Prussian," he said. Probably the most confusing thing to teach a kid... nations... and their personifications.