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As a father I must apologize for the boys' costumes. As you can easily tell, Milo's Batman costume is based on "The Batman" series running on the former WB and CW networks from 2004-2008 and Joey's Robin outfit is based on the Robin character from Cartoon Network's "Teen Titans" that aired from 2003-2006.
The most significant inaccuracy in these costumes is that Robin was never a character in "The Batman" series and inversely Batman was not a character in "Teen Titans." Therefore... technically the two superheros would never have appeared together in these exact costumes.
Other than that it was a pretty good Halloween!