As previously noted, there are cruise lines that are child free. Also, there are lines such as Windstar that restrict smaller children, but allow older kids with the caveat that parents are responsible for entertaining their child. In general, it keeps most adults with kids, off.
Now, as far as the OP indicated, they went at one of the worse times possible for the kiddos. Schools break between Palm Sunday and Easter increasing the likelihood of a large number of little people on board. But, here is the beautiful thing: traveling a week or 2 before/after will result in reduced fares and smaller crowds. I planned my (almost) birthday cruise around Christmas by selecting the week before winter break which means lower fares and fewer people.
If you are unhappy with HAL, that is fine. Cruise lines are businesses and their first priority is the shareholders with customers a distant second. The best way to get their attention is by hitting them at the bottomline and spending your money with a line that meets your expectations. If there is enough of a downturn in revenue, they’ll pivot.