One of the unexpected consequences of the structure of society is that males and females are incredibly divided over matters of behavior and relating. When my daughter was born, I counted myself lucky that I had 13 years to figure out how to address the entire males vs. females divide. I was very, very, wrong.
Each and every time there is a family party, or a social gathering of any nature, where there are male children near my child's age - someone inevitably says "Oh, Dahlia! How's your boyfriend? He's so cute, you might just have to marry him!" To be sure, at this point I am internally trying to stifle upchucking my Thanksgiving Tofurky. There are so many problems with this, that sometimes I can't even wrap my mind around someone's mental process that brings them to the point of awkwardly disregarding her childhood (this is especially pertinent when people tell her she looks "sexy" when she wears dresses. UGH!).
First of all, I don't want her to think of male creatures around her age as her only possibilities for pair bonding. It would be incredibly screwed-up and hypocritical of me to try to train her to be heterosexual, and since kids do not have expressed sexuality, any indoctrination about her "future husband" or "babies" would be exactly that. She may grow up to be a childless lesbian, and I don't want her to feel like she's betraying my stupid expectations of her, simply by living her life honestly. I don't name brand the type of car I expect her to own, and I haven't arranged a marriage/career/living situation on her behalf... so why should I do that about her relationships or procreation? Answer: I shouldn't. I expect her to do the best she can in matters of learning and education, promptly address her own problems in a dignified manner, and to be polite/mannerly unless someone gives her a reason to do otherwise. I don't have a husband picked out for her. I haven't frozen her eggs at birth to engineer the most attractive and fertile children. I may be a little wacky by today's standards, but not like that.
Secondly, I don't want her to feel obligated to view boys as these creatures she has to be shy around, to alter her appearance for, or to feel generally disconnected from - instead of just as "other people." I want her to be friends with boys, to laugh and learn with them, to find out their inner workings, to relate to them. Basically I want her to view them the same way as she does girls. Because until she hits puberty and starts to have sexual feelings... she should! Potential friends, confidantes, partners in crime. Not just walking potential husbands. Ever since my husband convinced me that marriage partners should be friends as well as spouses, I've seen the value in that. I always sort of vaguely looked at people I was in a relationship with as begrudging add-ons, rather than my friend. It was too risky, in my estimation, to be friends with a lover. Too much to lose, I needed lots of separation. If you never have one male friend, can you start with your husband? Same with a wife!
And last. I don't want her to fall prey to the idea that men and women are totally different creatures with different "hardwired" brains who have acceptable bad behaviors because they're not able to do otherwise. It's not THEIR fault, it's not MY fault, our brains are wired differently! My husband HAS to cheat on me, and I *have* to nurture our children while he's gallivanting, because he's incapable. I cannot stop myself from taking comfort in romance novels and ignoring the sex drive of my spouse because I'm a GIRL, duh! Decisions? What are those, I can't hear you over the sound of my own vagina! In fact, I can't do anything except babysit and crochet because, you guessed it, I get my period every month. Poor husband will never stop being able to carry every heavy object in sight for me, because I need help. I'm his dainty little flower! NO ESCAPE. It's brain science. Womp womp.
So, the moral of the story is: if you see a girl and boy playing together, encourage them to find all the things they have in common. Don't pretend-marry them, don't make them feel awkward, and they're not K-I-S-S-I-N-G off in the hilly brush somewhere. They're two tiny incomplete humans who want to build a friendship, let them. Let them explore their differences instead of pushing it on them.
Boys will NOT be boys, and that's the shitty punchline for every sad joke ever told in a creepy misogynist narrative, and it needs to stop. "Oh, she's just a girl" needs to stop too. Don't alter your expectations for your children based on their genitals. That includes expecting them to date/marry/procreate with someone of the opposite sex, either. Let them live up to their own potential, not the potential you decide for them.