your cruiseline will have guidelines

I guess you are either going with Carnival or Royal Caribbean as only they offer such short cruises.

Please remember you need to tip on a PER PERSON PER DAY basis - and children are counted as a PERSON. If your kids are small ones, you should tip MORE as they create more work for your cabin steward.

Please DO NOT SKIM YOUR TIPs - too many Chinese dont tip properly and make a very bad impression - which create a bias in service industry and becomes a vicious cycle. - Service industry employees see too many Chinese dont tip, so they dont provide good services as they expect the worst case, and then re-inforce those Chinese who dont tip, saying I dont receive good service, blah blah blah ...