You seem to want to write this off like we're all small children and have no ability to rational thought. You can be under questioning by congress while under oath and receive a question that would require revealing of sensitive information. At that point, you can lie like a small child, or inform the congressional panel that the conversation is approaching sensitive material and in order for questioning to continue, it would have to be done in a private session.

Please, don't treat me like I'm an imbecile. That's congress' job

Edit: also, that's such a shit parenting job. take the opportunity, and tell your significant other that it's not time for cookies and it'll spoil your dinner. there's no reason to lie about it. you have a teachable moment, and you've chosen to teach that it is okay to lie rather than something more valuable.

Part of the reason it's illegal to lie to Congress is that you are at the same time lying to the American public, who are the people Congress answers to.

It would be like lying in a deposition in front of the board of directors and then going back in private to your friend the line manager and saying "hey, that thing I said when it really matters was a lie because I didn't want the board to find out about it."