This is from a New York Times Op-Ed piece from Peggy Orenstein:

Among the “10 characteristics for Lego” described in 1963 by a son of the founder was that it was “for girls and for boys,” as Bloomberg Businessweek reported. But the new Friends collection, Lego says, was based on months of anthropological research revealing that — gasp! — the sexes play differently.

While as toddlers they interact similarly with the company’s Duplo blocks, by preschool girls prefer playthings that are pretty, exude “harmony” and allow them to tell a story. They may enjoy building, but they favor role play. So it’s bye-bye Bionicles, hello princesses. In order to be gender-fair, today’s executives insist, they have to be gender-specific.

As any developmental psychologist will tell you, those observations are, to a degree, correct. Toy choice among young children is the Big Kahuna of sex differences, one of the largest across the life span. It transcends not only culture but species: in two separate studies of primates, in 2002 and 2008, researchers found that males gravitated toward stereotypically masculine toys (like cars and balls) while females went ape for dolls. Both sexes, incidentally, appreciated stuffed animals and books.

Human boys and girls not only tend to play differently from one another — with girls typically clustering in pairs or trios, chatting together more than boys and playing more cooperatively — but, when given a choice, usually prefer hanging with their own kind.

Every experience, every interaction, every activity — when they laugh, cry, learn, play — strengthens some neural circuits at the expense of others, and the younger the child the greater the effect. Consider: boys from more egalitarian homes are more nurturing toward babies. Meanwhile, in a study of more than 5,000 3-year-olds, girls with older brothers had stronger spatial skills than both girls and boys with older sisters.

Score one for Lego, right? Not so fast. Preschoolers may be the self-appointed chiefs of the gender police, eager to enforce and embrace the most rigid views. Yet, according Lise Eliot, a neuroscientist and the author of “Pink Brain, Blue Brain,” that’s also the age when their brains are most malleable, most open to influence on the abilities and roles that traditionally go with their sex.

Traditionally, toys were intended to communicate parental values and expectations, to train children for their future adult roles. Today’s boys and girls will eventually be one another’s professional peers, employers, employees, romantic partners, co-parents. How can they develop skills for such collaborations from toys that increasingly emphasize, reinforce, or even create, gender differences? What do girls learn about who they should be from Lego kits with beauty parlors or the flood of “girl friendly” science kits that run the gamut from “beauty spa lab” to “perfume factory”?

At issue, then, is not nature or nurture but how nurture becomes nature: the environment in which children play and grow can encourage a range of aptitudes or foreclose them. So blithely indulging — let alone exploiting — stereotypically gendered play patterns may have a more negative long-term impact on kids’ potential than parents imagine. And promoting, without forcing, cross-sex friendships as well as a breadth of play styles may be more beneficial. There is even evidence that children who have opposite-sex friendships during their early years have healthier romantic relationships as teenagers.

While I think there’s merit in advocating for more gender-neutral marketing and packaging of toys (I have more than once ranted to anyone who will listen about how Scientific American magazine can be found only on the “Men’s Interest” rack at SeaTac airport), as someone who has an interest in both toys and development, I’m less concerned with the specific traits of the object and more interested in helping children explore the full range of emotional themes and developing ideas with creativity and complexity. Certainly there are toys that more readily afford this, but toys are only the medium through which a child expresses their own ideas and emotional life. I’ve witnessed (and been) a pink-clad princess who fights off mean witches and defeats crocodiles and observed a tender moment between superheroes. The limitation is not in the toys or in the child, but in the expectation of them.