"Gullible military children"... your words, not mine.
But let's expand on that; also your words: "Military personnel have the right and obligation to disobey an unlawful order. We are taught that in basic training." Okay, so... if there's no danger of an unlawful order being obeyed, there's no need to include training concerning duty to disobey. Now, does that mean that the aforementioned Congressmembers were acting out of the kindness of their hearts? Maybe a little.
There's also the probabilities that their actions were both a subtle reminder to service personnel there are consequences for obeying an unlawful order and a calculated gambit aimed at provoking the current head of the military into demonstrating his disregard for the Constitution, thirst for dictatorial power, desire to have anyone who speaks out in favor of rule of law and/or against his dishonestly self-alleged total authority executed -if it was the latter, they nailed it.
And, if the latter, as a li'l bit of maybe unintended bonus, they drew all the people who would nod along, defend, repeat calls for execution over reminders of the law into the light.