Car seats for a rental are not something this guide can confirm
If your plan includes renting a car, do not assume a car seat will be provided automatically. Current research behind this guide does not confirm Korean car-seat law or requirements, nor whether Jeju rental companies supply seats as standard or as a paid add-on. Request a car seat explicitly when you book, state your child's age and size, and confirm directly with the rental company what Korean car-seat requirements apply and whether their seat meets them, rather than assuming a seat provided at pickup will match what you'd expect at home.
Bus tiers matter more with young kids than they do without
If you're using Jeju's public buses rather than a car, the same three-tier color system that applies to any traveler applies to you, but the tradeoffs land differently with young children. Green village buses, which serve smaller and rural stops, are the tier most likely to involve a long wait, and a long outdoor wait is a bigger problem with a tired toddler than with an adult traveling alone. Building your day around red express and blue intercity/city routes, and treating green-route stops as a lower priority or a shorter side trip, keeps waiting time down where it matters most.
T-money and child fares: confirm the specific rate yourself
T-money cards work the same general way for children as for adults — buy or reload them at convenience stores, and use them for the same free-transfer benefit (up to twice within 40 minutes) described for any rider. What this guide does not confirm is a specific child fare rate or the age threshold at which a lower fare applies, since that detail wasn't available in the research behind this article. Ask at the point of purchase, whether that's a convenience store or a transit center, rather than assuming a specific discount applies.
Pacing: plan for fewer stops than you would without kids
Jeju's attractions sit far enough apart that a full, ambitious day of sightseeing already takes real transit time for any traveler; with young kids, that travel time compounds with the need for breaks, meals on a more flexible schedule, and simply not overloading a day with transitions. This connects directly to the car-versus-bus decision already worth making before you arrive: whichever option you choose, planning two or three stops in a day rather than four or five tends to hold up better with young children, especially on any day that includes a green-route bus segment or a longer drive.
What usually goes wrong
The most common planning gap for a family trip isn't the big decisions — it's the details that don't get confirmed until you're already there: a car seat that doesn't fit as expected, a fare rule you assumed rather than asked about, or a day plan that looked reasonable on a map but underestimated how long waiting and transitions take with kids. Confirming the car seat and fare questions above before you travel, and building slack into your daily plan, addresses most of what tends to go wrong.