From my experience over the past ~22 months, you won't get an option to do anything online if you have a lap infant.

In addition, get used to horrible experiences on the ground and in the air with UA, when traveling with an infant. On every itin, we've had to deal with the kiosk asking us if we have an infant, even though they have always been added to the record before leaving, and if we're on a solely international flight (when they are required to have a ticket), it still asks. Awful.

In addition, i've already complained twice to the DOT for a failure to refund miles/dollars for a cancelled ticket, and I will file yet another set of complaints tomorrow morning for UA not refunding a simple DTW-IAD, no complex routing, no international trip, no nothing...but since we had a lap infant, UA can't figure out how to deal with it.

Quite simply, UA is easily the worst airline i've dealt with when having an infant (our daughter is almost ~22 months old, and we've got another on its way), and we are both getting away from UA entirely, for this reason and so much more...

Call in to UA, and if you are lucky, you'll get a somewhat competent agent on the first try, otherwise, it's in your best interest to hang up and call again...otherwise, you'll spend a long time on the phone for the *fake* elite agents that have no clue what real world problems are.

-jeremy