So Conner and Tim just happen to have a Robin costume cut to fit Conner, who as was pointed out is much larger and more muscular than Tim? Uh-huh, sure.
Unless it was left over from the Teen Titan's "Robin Day," where the whole team went around in Robin costumes. Then I can dig it. (They had a "Starfire Day" the next week. Wrap your head around that one.)