If my math is correct 24kg is about 52lb so you should look into the inflatable Bubble Bum booster. It meets and exceeds both US and European safety regs. It's for kids 4 to 11yo and 40 to 100lbs. They sell them on
Amazon. That way you won't have to worry about taking a specific mode of transportation like a bus and could take a shuttle van, car service, etc.
A few years back we used CocoaBeachShuttle dot com to get from the Airport to the Port and back but they also service Disney. It was actually part of a hotel package as to how we found them. The Radisson At The Port in Cape Canaveral had a special room rate that included a OW trip from the airport to the hotel. We also booked them back from the Port to the airport as they were very reasonable.