Hate United. We booked tickets (to Denver) and they did not sit me (even though we booked to seats together) with my 5 year old.
I bluffed and walked away from my daughter and told the flight attended best of luck. She seemed surprise that I would not pay to upgrade to economy plus and asked was I "really going to leave my child alone"
Yes. You told me you "couldn't do anything" so - deal with it.
And just like that, they were able to correct the mistake.