If you’re taking a shared shuttle bus, it’s a bit inconsistent. Some have seatbelts, some don’t and even when they do, they’re standard adult seatbelts, not designed specifically for young children
For private cars, seatbelts are always available

You can ask the transport provider to arrange a child seat, but it usually costs extra and availability can vary. So it’s not always guaranteed

A practical solution is to bring a portable seatbelt adjuster for kids. They’re small, easy to install, and work with standard seatbelts.

bringing your own setup is the safest and most reliable option. That way you don’t have to depend on what the vehicle provides

thanks for your advice