Children don't usually need a passport or photo I.D. for domestic flights; however, it's not a bad idea to have photo identification for your children when you travel together. All airlines require the same documentation for children as they would for an adult on international flights.

For a 3-year-old to fly domestically within the United States, they do not typically need a government-issued photo ID, as the TSA does not require identification for children under 18. However, they must have their own purchased seat, as the "lap child" option expires once a child turns two. You will need their boarding pass, which can be digital or printed. For international travel, a valid passport is mandatory regardless of age, and some countries may require a visa or proof of relationship (like a birth certificate), especially if only one parent is traveling. While not legally required, the FAA strongly recommends using a government-approved car seat or a CARES harness to ensure the child is safely restrained during turbulence. Additionally, packing "sanity essentials" is vital: a 3-year-old will need noise-canceling headphones, a fully charged tablet with offline videos, plenty of non-messy snacks (to help with ear pressure during takeoff and landing), and a change of clothes in your carry-on in case of accidents. Most airlines allow you to check a stroller and car seat for free at the gate or ticket counter.