Once there is "an actual" case of norovirus the ship does go into a "lock down" situation. All food is served in the lido, salt and peppers are removed and everything is decontaminated. If you saw that then it's time to be suspicious.
Even when a ship does have an outbreak it doesn't go into dry dock. The worst that happens is that it may miss a run of a cruise and go through a sanitation process but usually once the crew goes through their illness and the passengers leave so does the virus.
Multiple hand washing and not shaking hands are the best thing you can do to avoid it.
I find it strange that the mother would have a child taken away. Perhaps the child was an adult who was confined to their cabin. If a minor is confined to their cabin one of their parents or adult guardian is confined with them.