Seattle-Tacoma is a well-organized airport, and traveling through it with children is manageable. The transport decision is where things get more nuanced.
The car seat situation
Washington state requires child car seats for children under 8 years old (unless they are over 4 feet 9 inches tall). Taxis and ride-hailing vehicles are technically exempt from this requirement under state law, but exemption from the law does not mean exemption from physics. If you want your child in a proper car seat, your options are: bring your own, rent one with a rental car, or book a private transfer and request a seat in advance.
Standard taxis at SEA do not carry child seats. Uber and Lyft drivers do not carry them either. Some transfer services can provide them if you request at the time of booking — confirm this directly with the provider.
Light Rail with kids
The Link Light Rail is stroller accessible and has space for wheelchairs and large items. During off-peak hours, it is a reasonable option with kids — the 40-minute ride is smooth and predictable. At $3 per person (children under 6 ride free), a family of four might pay $9 total.
During busy hours, the train gets crowded. Managing a stroller, multiple bags, and small children in a packed train is not enjoyable. You will be competing for space, and there is no guaranteed seating. If you have car seats to transport as well, the Light Rail becomes impractical.
What works for families
For families with children old enough to sit unassisted and no car seat needs, a taxi at the $40 flat rate to downtown is simple and effective. One vehicle, straight to the hotel, done.
For families with infants or toddlers who need car seats, a pre-booked transfer with a seat request is the most reliable approach. The car seat is ready when you arrive, the vehicle accommodates your luggage, and you avoid the parking garage navigation with loaded-down kids.
For larger families (5+ people), a transfer in a minivan is often more practical and cost-effective than two taxis.
Inside the airport
SEA has family restrooms with changing tables throughout the terminal. Nursing rooms are available in several locations. There is a children's play area near the C gates, though this is more useful for departures than arrivals.
Food options in the baggage claim area are limited. If the kids are starving after the flight, you will find more options before you leave the secure area. Once you are at baggage claim, grab-and-go options are minimal.
Timing advice
If you have flexibility on arrival time, aim for mid-morning or early afternoon. Traffic on I-5 is lighter, the Light Rail is less crowded, and the drive to downtown or surrounding areas is at its shortest. Avoid arriving during the 4-6 PM window if possible — the combination of rush hour traffic and tired children is not a recipe for a pleasant first hour in Seattle.