They don't use the term "self-guided", but only words about "without an educator." The ticket price is so low that I presume this is not the issue for you. In any case, it is easy enough to drop off your tour group and continue on your own if that is what you wish to do. That is, it's not like a "visit only by tour group" location.
Naturally, you would need to be prepared with a guidebook and a plan to make the most of your time at the two camps. Both sites are extremely large, and hard to understand without background and descriptions. You will have to find the barracks exhibits that pertain to your interests, and the other places that you consider suitable for your children.
I consider it ill-advised to ignore the OFFICIAL advice about children's ages. You are risking not only their comfort, but possibly the comfort and experience of other visitors who may have to endure the upset reactions of your children. This is a self-indulgent decision. Sorry to be blunt, but you are not the first person to make this mistake. Your decisions have consequences for others, too.