Wow, thank you for this question and for your inspiring desire to prepare your children to follow Christ in this post-Christian climate. The short answer is that I cannot think of a resources off the top of my head, so I will do some digging and get back to you soonest.
A few thoughts have popped to mind while reading your post.
First, it feels to me the most important thing we could do for our children is to teach them (in word and example) to love the Lord with all their heart, soul, strength and mind. Apologetics will only be effective built on a foundation of genuine relationship with God, meaning that the priority will be inviting them into this dynamic relationship. And then continuing to walk with them as they ask questions, make decisions, and mature into pre-teen and then adolescent years.
Second, it is helpful to teach them from as early as it is appropriate that they will come across different opinions, views of the world and people. This will take away the shock factor and, if communication lines remain open, they will be able to express hurt, frustration, confusion etc. to parents when the moment occurs. Hopefully, this will also mean they will be better prepared to make friends with people who are different and communicate with them. This is much needed in today’s society.
Third, it is fantastic if children can grow up knowing that it is totally ok to be open about their love for God and faith in Christ with others (even strangers). No shame or fear attached to this whatsoever. Perhaps there will be necessary growth in the approach to sharing, but rather the openness to do so and have to be corrected than be terrified of being ‘found out’ as a Christian and so remain silent.
Thanks again Curran, I appreciate your question a lot. I will attempt to find a helpful resource and get back to you. Perhaps someone will read this thread and know of something already.