I'm also curious about this. I had previously read under 3 was free if sitting on a lap. Disney Fantasy, are you referring to the cruise fare or transfers?
DCL Transfers do not charge for infants. I believe under 3 is no charge for the transfers. I personally have not experienced transfer buses with seatbelts that can accommodate a child's car seat. But I have heard there are some; however I don't believe car seats are required on any coach buses even if seatbelts are available.
We booked the DCL transfer for our 18 month old. There was no charge for him. A car seat is not required by law for the buses. I do not know if they could accommodate one or not.
I would imagine that the charge would only apply if they were taking up a seat (either on their bottoms or in a car seat - though I don't know how you'd attach it).
If you aren't charged for them, you'd be expected to hold the under 3 in your lap. Because otherwise they're taking up a seat that someone paying could use.
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