We appreciate the sensitive nature of this question.
1) While the modern day norm is for people to marry in their 20's and even older, the average age of marriage has varied in different eras and cultures. Historically marriage has taken place as early as age 12. It would be unfair to state that Hashem created an untenable situation. Nevertheless, given the current societal norms you raise a valid concern. Children begin to physically and emotionally mature long before we treat them as full-fledged adults. This raises frustration in many areas beyond the issue of sexual exploration and sexual urges. Rather than dwell on the problem, our role as parents is to try and guide our children and teach them how to best navigate the complex challenges of growing up.
In this respect, it is important to find healthy outlets for our kids' need of physical touch and affection. Maintaining physical affection with our kids is important for parents to continue even as our children grow older. Sports is also great physical outlet and helps kids release energy and frustrations. While generally more common among girls than boys, kids often can express non-sexual physical affection within friendships.
2) Children need to learn boundaries and self-control in many areas beyond sexual urges. Unless they are taught otherwise, most children will freely lie, steal, hit, etc. We need to teach our children the difference between right and wrong. We need to teach by word and by example how to overcome temptation and keep mitzvot despite our natural inclinations. This is an also an opportunity to teach our children about teshuva. We are just human, we all make mistakes. You should talk to your kids how this can be very challenging, and if they do succumb, they should not give up, but continue trying to succeed and improve themselves. Each time they overcome their urges they have made tremendous progress and should be proud of their accomplishments.
Furthermore, while children are responsible for keeping mitzvot from the age of 13, halacha recognizes that this is just a starting point and, according to most opinions, they are not liable for divine punishments until the age of 20. Halacha recognizes that teenagers are still maturing and are not held fully accountable for their actions yet. This is the period in their lives where they learn, through trial and error, about how to be responsible and mature adults, capable of fulfilling their obligations to Hashem and to others.
3) We do recommend that you (or your husband) talk to your teens/pre-teens once they start physically maturing. This topic can be brought up in the context of a general conversation about sexuality and growing up. Obviously the content of the conversation will vary with your sons and your daughters, and depending on their personality, maturity level, etc. Your sons should be told clearly, yet gently (no need for fire and brimstone) the prohibition of hotza'at zera l'vatalah. You should explain that some things are in their control and should be avoided (active masturbation/touching), while other things (wet dreams, etc.) are beyond their control and they are not held accountable for them. Be prepared to answer questions openly and honestly. You may find the book Talking about Intimacy and Sexuality: A Guide for Orthodox Jewish Parents, by Dr. Yocheved Debow, to be helpful in preparing for and navigating these conversations.
You have to find a healthy balance, teaching your kids to distinguish between right and wrong without pressuring them or making them feel guilty when they find it difficult to meet these expectations. Gentle comments are more helpful than fierce reproval. Focus on the positive, on their accomplishments, and be prepared to overlook their many missteps and mistakes.
May you have much hatzlacha in raising your children to be healthy, well adjusted, committed Jews.