Kids grow up and soon as they are able to, the ones that question things start looking for information. If they can't get the information they need (not allowed, no access, etc.), as soon as they turn of legal age, the hunt begins for some of them. For others, it doesn't begin until later -- but for many, the hunt will begin.

Leave a trail for them to find. Letters. Videos. A diary. Something. But leave it for them to try. One friend I have, has a box with every letter he ever wrote to his daughter, all of them returned to sender. But, there you have it -- proof.

Leave the trail. Let the chips fall where they may. If the child doesn't accept it when they are grown, you tried and there is proof that you did. You did the right thing.