Originally Posted by
jsloan
I believe that the only thing that is actually promised is that if there aren't two seats adjacent, UA will put the passengers on the next available flight at no charge. They generally won't move passengers around without asking; and while some gate agents will call other passengers up to the podium to ask if they'd swap, many delegate the responsibility to the parents.
There's a little more to it than that. They'll waive fees, that would otherwise be charged, to select adjoining seats to accommodate the child. Here's the policy from the website.
If you’re traveling with children under 12, they won’t have to sit by themselves. The first adult listed on the reservation can sit next to up to two children in their party for free. After you book your flight, you can select these seats in My trips. You can also choose your seats by going to the seat map in the United app and selecting “Seat preferences”. We will show you all available Basic Economy and Economy seats. The rest of your party may be given seats in a different part of the plane. To make sure your entire group stays together, consider paying to select seats for everyone.
Sometimes, seat assignments change because of unscheduled aircraft changes. If this happens on your flight, and your children are separated from an adult, you can switch to another flight with open seats in the same cabin for free.