I think you are going about it the right way. You can take the test if your kids need it for medical reasons some day. There is plenty that makes one a parent apart from passing on one's genetics. Your kids consider you their father and trust you explicitly. That is the strongest bond there is-one of love and trust. Unless you are going to take some call after the results like entrusting them to their mother or their biologic parent/father if God forbid the results are not what you want them to be, I don't see any point in this exercise. If will only sow more seeds of confusion and spoil all the wonderful memories you have with your kids. Don't do what is best for you. Do what is best for your kids. That is what good parents do and you already know what and who is best for them.