HAL seems kid-free because it does have well-behaved children when they are on board. I think the tone is set by the ship and the parents who choose HAL and it works. I would not want to see HAL encourage more family travellers at the price of losing that prevailing sense of quiet enjoyment by those both young and old enough to appreciate it. I think you know what I mean.
Holiday cruises are kid-friendly times and the higher level of young energy is to be expected at those times.