Yes on NCL you can adjust the Service Fee. From their website
In the unlikely event we cannot satisfactorily resolve the issue through our guest satisfaction program, guests will be able to adjust the service charge according to the level of inconvenience they feel they have experienced.
Hopefully you won't have to. I can't imagine any reason to warrant this. We have always had decent service and tipped extra when exceptional service was given.
MomX5, here is a guideline for families. Maybe this will help you.
$10 per person, per day will be added to your onboard account. For children ages 3-12, a $5 per person per day, there is no charge for children under the age of three.
I remember tipping well when we cruised with our 3 sons but we also kept the cabin very clean and neat.
We just think of tipping as just a part of the cruise.
Teresa and Larry
#36-Carnival Splendor 9/16/12
7 night Mexican Riviera
#37-Allure of the Seas 11/11/12
7 night Eastern Caribbean
#38-Celebrity Solstice 4/8/13
17 night Tahiti -- Sydney-Honolulu
40th Anniversary Celebration
270 days at see; soon to be 302