No. Passports are not required for US citizens to travel by air within the United States.
Yes, a passport needs to be signed before it can be used for travel.
Yes, a baby needs a passport for international travel.
Yes, a baby needs a passport to travel internationally.
Yes, a baby needs a passport to travel to Canada.
Yes, a baby needs a passport to travel to Mexico.
Yes, a child needs a passport to travel to Mexico.
Every child needs his/her own passport to travel outside of their home country.
Yes, a 2-year-old needs a passport for international travel.
Yes, a US passport holder needs a visa to travel to Australia.
Yes.
Anyone who plans to travel outside of U.S. needs a passport for travel. The traveler will need the passport to enter another country, and return to the U.S. Source: I am a passport and visa specialist with Visa Passport Pro - the leader in US Passport Expediting.
no