I can't help with the child part, but most lines do wedding / anniversary packages (usually in the special occasions on board type extras).
This cruise we're on NCL, and can get the room decorated, flowers delivered, or a gift basket (with dinner in one of the pricey restaurants). There's also a honeymooner's party we were invited to. On our registration form (and the on-line travel agent asked too) they asked if we had any special events (anniversary, retirement, birthday..) and what day it was. I know I looked and most lines have something they can do.
We did my birthday onboard a couple years ago and they did a cake to the table (assigned dinner tables, not freestyle cruising). It was done a day late because my birthday was embarkation day and dinner was random seating that night.