In addition to being possibly one of the best people on Twitter, we're pretty sure that former child star Mara Wilson is on the cusp of becoming one of our favorite new writers.The Matilda actress has a book coming out in September, entitled Where Am I Now? True Stories of Girlhood and Accidental Fame. And while it's pretty clear from the name of the collection what she'll be delving into, we were pleased to discover that there will be at least one anecdote about her days on the set of Mrs. Doubtfire.In a recently released excerpt , Wilson writes about a particular day on the set during which she was just bursting at the seams to share a bit of newly gleaned knowledge regarding the facts of life. Her mom had recently given her the "sex talk," and the six-year-old actress was hellbent on keeping the conversation going on-set."I wasn't focusing on the scene. I was bubbling with excitement, because I knew this thing, this big open secret, and I could not keep it in any longer," she writes in the book. She ended up asking one of the hairdressers if she had ever "done it," and then breaking into a singsong announcement."As soon as she walked away, I announced in a singsong voice, 'I KNOW ABOUT SE-EX! I KNOW ABOUT SE-EX!'" she recalls. But while the crew thought all this was funny, her mom was totally humiliated. (Kids say the darndest things, don't they?)Robin Williams realized what was going on and relayed to director Chris Columbus that Mara was asking the crew about sex — and that's how a certain compliment worked its way into the script. While they were working on a scene in which Wilson helps Sally Field pick out a dress for her birthday dinner, Columbus told Wilson: "You know, Mara, if you want, you can tell Sally her dress is sexy." And the rest is screen-gem history.