Purim Costume Customs and A Philosophical Query

Come Purim, each person finds his niche. Some are great at Purim Torah, churning out a witty, thoughtful parody that makes its way around the interwebs. Others come up with clever themes for their mishloach manot, sending out lovely, tasty and inspiring treats dressed up as something else. (My favorite this year: we got a "plant theme", complete with chocolate mud cake, grass, a candied strawberry and even gummy worms.) Still others expends tremendous thought and energy designing, creating and even sewing clever costumes - especially here in Israel. It's not uncommon to see kids dressed in costumes created from scratch by their parents, er - mothers.
Not us. We now have our own costume custom: pull down the costume box from the attic, and see what we can pull out.
It's worked for the past couple of years, so why not this year.
Our son, Petachya, is almost five, which means that he's the perfect size for our Robin costume. First of all, this brought up a tricky problem. I took him to gan in costume on Friday, and they asked me what he was dressed up as. I said "Robin." In the States, I would have gotten a knowing look, an "Oh, how cute," and moved on. Not here. The gannenet gave me this puzzled look, as in, "What's a robin? Isn't that a kind of bird?", kind of shrugged, and we moved on.
In any case, when putting on his costume Petachya wanted the whole getup, including the belt and cape. When he started "flying around", we had to, of course, explain to him that Robin could not actually fly.
Which only made us wonder: if Robin couldn't fly, why did he wear a cape?
Why indeed?