Kids & Halloween Costumes: The Struggle is Real

We've been talking about this year's Halloween costume since, I don't know, our post trick-or-treat candy sorting session last October 31st.  The costume choices have changed about 437 times, and continue to vary from princesses to monsters, and everything in between.

We were on a Little Mermaid kick for a while, so I went out a bought the dress, the wig, the shoes, and now she's anti-Ariel.  Awesome.

Then she heard a few of her friends talking about being cats and jumped on that train, so I thought about a DIY costume, then I remembered that i'm totally not a pinterest mom and would end up hot-glueing myself to some homemade cat ears and wind up in the ER.  Next.

Who knows what she'll come home from school asking for next.

So, parents of the Hudson Valley, i'm looking for some help - is there a cutoff date for costume selection?  Do you pick out costumes for your kids?  At a certain point do you put your foot down and say you're going as this, or not going at all (oh man, I TOTALLY just channelled my mom with that last one).  Help a toddler parent out here.