Had an interesting experience yesterday, and would like to better understand what should have/could have been done should I ever run into a similar situation in the future. Mods, this also pertains to traveling with children, so feel free to move/cross-post, but it happened on United.

My family were traveling MSN-DEN along with my sister-in-law and her two kids (ages 2 and 4) who were traveling MSN-DEN-BUR. All on United. We arrived to MSN a few minutes apart so we were reacquainted at the gate. When we get there, my sister-in-law is in tears and walking away from the gate agent. On the MSN-DEN flight she was given 2 seats together with the 3rd seat in the row behind. On her second flight she was given 3 seats each several rows apart from each other. Some background, I didn't book her tickets, but she booked them through Expedia and it sounds like they were Basic Economy fares, though I'm basing that solely off the gate agent saying "the fare type she booked does not allow seat changes." Sister-in-law claims she couldn't select seats after making her reservation, though admittedly she's not the most savvy at this (clearly) and as a busy working mom was no doubt in a rush, so who knows. Anyway, she was a mess so I offered to discuss with the gate agent on my sister-in-law's behalf. The gate agent was...prickly, to say the least. Neither flight was full, but she claimed due to the fare type it was impossible to give her seats with her two minors. I gently reminded the gate agent that unrelated to United's fare policies there's actually a federal law that prohibits minors being split apart from their parents on planes. She looked at me and simply said "It's not possible." Great customer service. I tried again a few minutes later with a different gate agent, and although he was much nicer, it was clear he was out of his element, so I dropped it.

We boarded the plane and with the help of the flight attendant they managed to move seats around (we couldn't help as we were ~7 rows away) so she could sit with her kids, though one unrelated gentleman unfortunately needed to switch from an aisle to a middle to accommodate and was (rightfully) not not pleased. When we landed in DEN we accompanied them to their next gate and that gate agent easily and happily moved seats around to make sure she had three seats together on the second flight.

As we sat on the tarmac waiting for a thunderstorm to pass I quickly looked at the Families Flying Together Act and found it to be extremely unclear. Was United violating this law? Should the gate agent have switched her seats to comply? Does in-front/behind count as together? Although it all worked out I'm wondering what happened here and how to deal with this in the future should this ever happen to me or someone else I know. Thanks!