We addressed our kids together, it was a family talk. Both of them present and both of us present. We even talked about hormones and "when your sister seems crazy or cries all the time" and "when your brother runs out of tissues). lol We had funny moments and the kids offered some serious questions. We were honest. We talked about bodily fluids and compared them to snot or phlegm. Some questions needed tweaking because they were misinformed (no, you can't get pregnant from setting on a toilet seat after a boy pees). Yes, mom did talk about "vibes" with Addy (who had already discovered her mother's! lol). She explained that she might be tempted to use things that can hurt her, and so if she felt she wanted or needed something like a "vibe" to just drop her a note or just ask. Noah really didn't get it entirely, but we explained it to him. He blushed, but he was all ears. We talked about posters, models, and swimsuit magazines. We talked about adult magazines and entertainment. We said that as parents, we set the tone of what is acceptable in the house and for whom. We warned them both that if we discover something that we feel is offensive or terribly inappropriate we reserve the right to throw it away without warning or notification. So, if it is personal and even might offend us, keep it hidden out of respect. They really seemed thankful that we talked to them about it. Kids crave attention, knowledge, and acceptance. They found that in our talks.
We started talking about the birds and the bees at 6. We have pets. So they had questions about "What is Charlie doing on Farrah??? What is that on Charlie???" That helped. We left 7 open with periodic references to "making babies" when watching television and the subject presented itself. We also began talking about love and bonding as it relates to marriage and sex after marriage. Plenty of opportunities in Disney films about various princesses and princes seeking marriage. At 8 we opened up a little full bore and we're leaving the rest of 9 and 10 to open several subjects again as necessary. It was funny, we were watching Transfomers and there's a seen where the mom asks her son if he was "masturbating". That opened up a few questions. There are plenty of opportunities out there, you have to determine in yourself not to let them slip buy. If there is a love scene in a movie... mention it being normal for couples in love to want to be lovers... emphasize that it's so much better if they wait until after marriage though because most movies don't depict married lovers as often.
The point is... many wait until puberty starts to have the talk. But by this time kids are feeling awkward, embarrassed, self-conscious, private, etc.... so they won't open up to you. You have to catch them when it's a friendly conversation with kids who aren't feeling so personally embarrassed or ashamed. If you don't they will close up on you, shut you down, lie to you, and do whatever they can to evade the topic. They will also feel offended that you are asking personal private questions and seeking to win "mommy points" or "daddy points" late in the game. Starting young keeps it light, matter of fact, and they ask the craziest questions without as much embarrassment because it doesn't pertain to them yet. In fact, they will leave you feeling embarrassed when they ask personal questions about you and what you do. lol
Lastly, be honest. Don't lie. Be transparent. Don't skirt the truth. They can sense it and it really causes them to get the "willies" about it all. Tell it like it is. Talk about many of the joys and pitfalls you've experienced. Talk about feeling ashamed or guilty about certain things and how you had to learn that God loves you as you are and made you like you are with this as a blessing. You certainly don't have to reveal too much. But lying isn't the answer. We chose not to disclose any indiscretions of our own prior to marriage (just being real here). We decided that it would be better to laugh and say, "My first time with daddy/mommy was a really special and interesting story, and it was very special to me, we'll talk about it after you're a little older." Beyond that... we're pretty open with anything the kids ask us.
We even started practicing "knock first" policy. We chide one another if we catch someone just barging into one of our rooms ("Bulldozer!!!").
So as it relates to ages and our strategy...
6 - General info. should they ask questions. If kids see pets mating, a simple, "They are trying to make a baby." is all that is necessary.
7- Revisit for questions. Remain open to opportunities in media to talk about sex being "natural", "beautiful", a "gift from God".
8 to 9 - Be frank. Talk about the more private issues (self-petting, menstruation, privacy). Show appropriate charts/illustrations/pictures (pics of STDs are very interesting to them and gives ample warning of what can happen). This is the first "big talk". Remain open for opportunities in media. Be bold, you're in charge and if you don't have this talk with them... who knows what information they will get and what they might think they know that needs corrected. You're children, your duty.
10 - Revisit the "big talk" and continue to focus on self-respect, true beauty, self-esteem, God loves you, grace, privacy, private items, respect for one another's privacy and mommy and daddy's privacy... dangers and pitfalls.
11 - Puberty will probably be an evident reality at this point. Now start reinforcing what you've said before with privacy, openness in communication, beauty, and how what they see is the changing... not the finished product, etc. Make sure son always has tissues in his room and that your daughter is well prepared for her personal needs, hygiene etc.
12 - They will most likely not want to talk to you much at all... unless you've built that comfort level and openness.
13 to 18 (and beyond) - Hopefully you've built a good report with them and can talk about the circumstances and issues they will be confronted with, needs they might have, feelings, mistakes, etc. If you haven't... expect to be kept in the dark and always be the last to know anything.
Be full of grace, patience, and understanding... (and did I mention patience?). Remember how it was for you growing up. It hasn't gotten easier for kids. It's only gotten harder. If they can't feel like they can turn to you without losing your love and respect.. who can they trust?