When you’re 7 years old, deciding what to be for Halloween is serious business.

After weeks of debate and deliberation, my daughter chose to be a mummy. The decision was final. My 10-year-old son, on the other hand, was less steadfast in his decision. He just needed to be gross and scary.

Armed with a plan, we headed off to the costume store that had popped up in our local strip mall. The excitement was palpable – my daughter was actually skipping as we crossed the street to enter the shop.

Greeting us was an energetic salesman, who asked if we were searching for a specific costume. My response was a simple yes: We needed a mummy costume. He glanced back and forth between my son and my daughter, paused, and asked, “A girl mummy or a boy mummy?”

To me, it seemed as if the store got quiet and the minutes got long. And I heard the inevitable deep sigh escape from my daughter. I looked down at her, and the only word to describe her face was crestfallen.

See, the problem is that I’m a research scientist who studies kids’ gender development. I study how marketing toys as girl toys and boy toys can change kids’ toy interests. My kids have heard me repeat that there is no such thing as a “girl toy” or a “boy toy.” They know that my research says that toys are important to kids’ learning, and that they should play with all the toys that they find interesting — not just the pink or blue ones or those from the boy or girl aisle.

And my guess is that they knew what was coming. Even if the young salesman did not. I asked the big question: “Is there a difference between a girl mummy and a boy mummy costume? Why should it matter?”

Instead of answering, the salesman asked who would be wearing the costume. When my daughter tentatively raised her hand, he whisked us over to the costume section labeled “Girls.” While his search for a girl mummy costume was coming up empty, my daughter was combing the aisles deemed “for her.” “Can I be this instead mama?” she asked, holding up a Roman goddess costume complete with a pink sash and gold jewelry. Of course my answer was yes. But I’m sure that it now was my face that was crestfallen.

While I walked up and down the “girl aisles” and “boy aisles,” I couldn’t help but think about a study I conducted a few years back on kids’ costumes. My research team and I got permission to watch local preschools’ Halloween costume parades. We coded how masculine and feminine 110 children’s costumes were. We had the parents of these children fill out surveys about how they chose their costumes.

We weren’t surprised to find that the girls’ costumes were much more feminine than the boys’ costumes. But we were surprised to find that the costumes became more gender-typed the older the children became. When parents were choosing the costumes, they were picking gender-neutral costumes, such as pumpkins. When the children were picking their costumes, the girls were choosing princesses with tiaras and heels, with the boys opting for superheroes with fake muscles.

Many factors influence children’s decisions about clothes and toys. Research shows that after age 7, many children conform to gender rules a little less (maybe explaining why when parents choose costumes they pick more neutrally).

But as I strolled up the “girl aisles” filled with princesses, police officer costumes with ruffled mini-skirts, and doctor costumes with pink scrubs — and then down the “boy aisles” filled with ninjas, bloody ghouls, and the same doctor costumes but with blue scrubs – the impact of gender-based target marketing was clear. Even on a holiday designed to let kids pretend to be anything they could imagine, there are still things girls are supposed to be, and those things are different than what boys should be.

And there in the girl aisle was my daughter. She had the goddess costume on over her grass-stained soccer uniform. Her neon-blue cleats peeked out as she twirled around the store for effect. She looked adorable, and I was happy for her.

But a part of me wonders how different the holiday would be if we stopped making gender rules and instead let kids’ imaginations run wild.

Lisa M. Dinella is an associate professor of psychology at Monmouth University in New Jersey. Her research examines the gender labels of toys and the impact of media on buying choices.

Like On Parenting on Facebook for more essays, advice and news. You can sign up here for our newsletter. You can find us at washingtonpost.com/onparenting.

You might also be interested in: