If you're kids are eating, showering, sleeping in a bed or creating any other work for the waiters or cabin stewards, then you should leave the recommended "tip" for each person. If you leave them at home, then don't tip.
Yes, tips add up to an expense at the end of the cruise, but these guys and girls work very hard to make your trip great and their primary income is your tip money (would you work 14 hour days for $150/mth + tips). Don't short change them!!!
Have a great cruise.