This is long-winded, but it gives the view point of talking to a son AND to a daughter, and about discussing different topics. It may be over-the-top for some, so my appologies an advance.
My husband and I are also open with our daughter and son, age appropriately. Our daughter knows all of the science of reproduction (yes, she's watched animals on farms mate). Our 6 yr old son knows how boys & girls have different body parts and their proper names, about privacy of each person's body and that it takes a Mommy and Daddy getting married before they're allowed to have a baby. We only answer the questions they ask and he's not interested right now. He has a "girlfriend" from Kinder last year. They both decided that they "love" each other. I know her Mom and we've talked about it. We've both told our kids: NO kissing, period! NO hugging, except after school when one of us Moms is there.
I have told our kids about being true to the other person. I'll tell my conversation with just my son since using "he/she told his/her girlfriend/boyfriend" gets real old, real fast and with him the conversation was simpler. I told him that since they have discussed and AGREED that they are a "couple", that a person can only have ONE girlfriend or boyfriend at a time. He cannot be anybody else's boyfriend while he is her boyfriend. If he wants to have a different girlfriend, he has to tell the one he has that he doesn't want to be her boyfriend anymore BEFORE he asks another girl to be his girlfriend. I told my daughter that she needs to follow this rule, as well, that it is not just the boys who have to be true. Also, that they can break up with someone if the other person is not true in return.
Our son has mentioned that he wants to have babies with his girlfriend when they grow up. I explained that they BOTH need to graduate high school first and that IF they still love each other at that time, THEN they can get married and THEN they can have babies.
My daughter will be 10 next month. This past school year (3rd grade), she and a boy she has been in class with since Kinder decided that they "liked" each other. On Valentine's she brought home the $1 Store flowers, heart ornament and teddybear keychain he gave her. It was really cute. I asked if she liked him back the same way. She said yes. I asked if it was because she felt she HAD to since he gave her the gifts or did she like him BEFORE he gave her the gifts? She said, "no, we talked about it last week." I asked her if they were boyfriend/girlfriend. She said yes. Had they kissed? "Eeewww, no, gross!" So far, so good. I explained that since I knew who he was AND his parents it was okay. They could hold hands SOMETIMES, however, there was to be NO KISSING. She said okay. I explained that I asked her those questions so that in the future she would know that she does NOT have to like someone or do anything she doesn't want to just because that person gives her something.
I know it sounds young to teach them that, but I feel that learning now to "be true" and "waiting" will save them some heartache later and help them to be better spouses (and maybe help with "the Talk" later as well). I can't stand hearing people say: "it's not an issue - my daughter can't date until she's 30, but my boy can have as many girlfriends at one time as he wants and he can start dating and doing "what he wants" with girls when he gets interested in girls - that's My Boy! What a Stud!" Hello! Who's daughter is he going to be dating at 11? Someone's 10 yr old daughter! So, my son and daughter are going to learn respect for themselves and others NOW.
No real dating until 16 for my daughter OR my son. They can hang out at school, and maybe the other child can go on outings with us as a family activity. I've agreed to discuss kissing at a later date, but NONE for now, and sex would be best saved for marriage, if possible. I was 17 and CHOSE not to wait for marriage (I haven't told her THAT yet), so I know it can be difficult to resist. We'll have the birth control/protection talk when that seems appropriate. My daughter asks questions earlier than most people feel she should, but it's hard to shield her when things are all over the commercials now AND she thinks AGES above most kids her age (her Gifted/Talented Teacher says that's normal for G/T kids and she'll always be ahead in things like that intellectually even though WE'RE not ready). She knows what the word condom is, but not exactly what the item is or is used for. She figured out the Viagra and the "makes men bigger" drug commercials (can't remember the name) all by herself! Ugh! If I feel the answers to a question are too old for her, she accepts when I tell her, "Sweety, MOM's not ready to answer that one, let me think about how I need to talk that one over with you." We have always been open with our kids about our bodies, that waiting until marriage for sex is best, that NO ONE has any right to make them do anything they don't want to and that they can talk to us about ANYTHING.
I hope some of this helps. We're in for a wild ride :)