Most hotels charge by the room (based on 2 people), doesnt matter if its 2 adults, 4 adults, 2 adults and 2 kids, etc. Some will charge more if you have 5 people and need a roll away, but the fee for that is usually pretty small, like $10 per day. For example if you book , thru disney travel, 2 adults at PP in May its 1264.08, if you add a child its $1427.08. That is $163 difference or about the cost of the childrens park hopper.
So, even if you booked just the adults you would still have the cost of tickets and as you said, airfare. The last few years they have offered kids stay free/ play free. One free childs ticket (3-9 years old) per adults ticket. Not sure if they would offer that in 2008 or not. That special typically runs from Jan- to mid April. Sometimes you can get kids fly free during that time as well. You have to watch the rates on that though- sometimes the adults fares are more then it would be to find a bargin rate for everyone.
