Is this a commonly used phrase like we would use "morning, noon and night" in English?
Di mattina - doesn't it mean 'of morning' and in english this could also be 'for morning'
Di mattina does literally translate to "of morning", but especially in this case, think of it just as "in the morning". To say that they make food "for the morning" would be Fanno/Preparano cibo per la mattina...per domattina...
Could this also be "They make breakfast, lunch, and dinner"? I didn't try it, but it seems like it might make sense. As in cibo di mattina is another way to say colazione.