I'm sorry we're coming across as unhelpful. We're trying to be forthright. In the majority of cases the TSA isn't too much of a problem. If they're being reasonable when you approach the checkpoint, you'll breeze through.

If they're being unreasonable, things will get very unpleasant. Because just about everything is SSI, and the TSA changes their demands of passengers arbitrarily in order to keep terrorists on their toes , we can't tell you what they do or do not require.

You can go to their website and try to get information, but be advised that many travelers have found that if the screener and/or his/her supervisor is/are being unreasonable, expecting them to adhere to what's published in their own "regulations" or on their website tends to lead to retaliation against the traveler.

I'm sorry we can't be all smarmy and encouraging. Reality being what it is, we can't tell you what to expect. If you had asked if you should load a child onto an aircraft to go to Boston, we could have been more helpful. Since you've already made up your mind to take this course of action, there's very little in the way of help that can be offered.

Will there be a 4th adult traveling with you? One of the things that seems to come up frequently is that the TSA preys on women traveling alone or with children. If the TSA demands a "private" groping session with one of you ladies, you're entitled to an escort of your choice. (The TSA won't inform you of your right, you must be aware of this right and claim in firmly.) If this happens, who will stay with the child while you ladies deal with the "resolution pat-down?"

As for the "requirement" for ID, I have found that traveling with your own child or seeking medical treatment for your own child often means encountering an illegal demand for the child's ID or SSN. While you aren't required to surrender either, it is usually easier to comply than to resist. The illegitimate "authority" is usually imagining that you're kidnapping your child from your spouse. The illegitimate "authority" isn't authorized or entitled to investigate such issues, but this won't prevent him/her from calling police or social services and making your interactions with him/her very difficult. For this reason I usually have my children's passports and social security cards on hand. It reduces drama. You might discuss this with your sister.