Whether you can pick your seats on United depends on the specific "Economy" fare you purchased. If you booked Standard Economy, you generally have the ability to select a seat for free at the time of booking, although "Preferred" seats (closer to the front) or "Economy Plus" (extra legroom) will require an additional fee. However, if you booked Basic Economy, you are not allowed to select a seat for free in advance. United will automatically assign you a seat at check-in or at the gate, and groups—including families—are not guaranteed to sit together. In 2026, United does allow Basic Economy passengers to purchase a specific seat assignment during the booking process or later via the app, but if you want the flexibility of choosing your seat without a per-segment charge, you must upgrade to a standard Economy ticket. Note that United has a "Family Seating" policy that aims to seat children under 12 with an adult for free, even on Basic Economy fares, provided there is availability.