While Hadrian was used to being on the road, and it was much more comfortable travelling in a carriage, the kids were constantly tired. Which meant they spaced out and complained they couldn't sleep.
That was also brought about by the fact that they needed to sleep during the day as they travelled during the night. Edwin, Hadrian suspected, was a seasoned veteran of four hours of sleep per day.
He had to be too, being a healer. Hadrian had to pretend to be asleep for longer as he literally restrained Edwin with his bulk.
The children, not wanting to hear Edwin write about the cases he had encountered on the road in the middle of the day, also piled on the healer.
Maybe Edwin had caught up on it and was keeping silent. Perhaps he was just obvious. But he kept still the entire day and tried to sleep, with varied success. Hadrian had the need of only six hours' worth of sleep.