Minors holding dual citizenship - using Canadian passport to enter/exit US [duplicate]

US law requires US citizens to use a US passport to enter or leave the United States. There is no penalty on the books for breaking this law, so if you show up in the US without a US passport for your daughter, probably the worst that will happen is you'll get yelled at and told to get her a passport. Usually the harder thing is convincing the airline to let you board your flight back to the US, but since she has a Canadian passport that may not be a problem either. So to my knowledge, you could probably do what you propose.

HOWEVER, it's quite possible to get a new passport within your timeframe if you're willing to pay a $60 expediting fee and are able to get to a passport agency before you leave -- see the US Department of State's webpage on the subject for details. That is the route I would suggest -- then you are guaranteed not to have any issues with this.

I agree that seeking an expedited passport renewal right now is the best course of action.

There is a significant possibility here that your daughter will be denied boarding the flight back to the US. Here's why: if an airline flies a passenger from one country to another, and the destination country refuses to admit that person, the airline is required to fly that passenger back to the departure airport at the airline's expense. Airlines want to minimize the chances that they'll have to do that, so they check passenger's travel documents carefully.

Airlines see what documents are required by entering passenger data into Timatic, an online reference. Here's a link to access Timatic. Canadians can enter the US without a visa. When checking in with the airline for your flight back to the US, you may be able to present your daughter as a Canadian citizen and have the airline allow her to board.

However, when offered a US Citizen traveling to the US, Timatic returns this text:

Passport required. - Passports and other documents accepted for entry issued to nationals of USA must be valid on arrival

Your daughter's expired US Passport is not "valid on arrival." Thus, if the airline thinks your daughter is a US citizen, or thinks she is also a US citizen, they may well refuse boarding. The airline might well think this, as she was born in the US and is accompanied by her whole family who're US citizens. There is a real possibility here that the airline will refuse to board her.

If she is allowed boarding, upon arrival in the US she will be screened by CBP to see if she is, in fact, a US citizen. Having an expired US passport will help at this stage, as will having a copy of her birth certificate. But it's still going to be stressful and time-consuming. Adults in this situation are frequently held for hours before being allowed to proceed. Even if you're successful and CBP believes she's a citizen, you'll be the recipients of the inevitable mean-eye lecture about carrying a valid passport and using it for entry and exit from the US.

All in all, start compiling the paperwork now and make an appointment at one of the passport centers as mentioned by ajd in the previous answer. You may be able to make an appointment over the net, and not even have to wait until tomorrow to call on the phone to make it.