RE: Best Disney resort for family of five (kids almost 5, almost 3, 4 months)
If you can splurge and not feel bad about it, I think the Contemporary is your best bet. You can walk to the MK and monorail to Epcot. I've never been able to bring myself to spend the money though!
The kids will enjoy any of them, so I really wouldn't worry about that. Since your youngest is an infant, they don't count in the headcount, so you can stay at any resort. When your youngest is over 2, then they count against your hotel headcount and your places to stay will be much trickier.
The Epcot area resorts offer the convenience of being able to walk to two parks, Epcot and MGM. Those are probably my older DD's favorites so that is where we prefer to stay. We also like to walk into Epcot most evenings and eat dinner there. I personally think Epcot in the evening is one of the nicest things about WDW. :)
The moderate hotels are significantly cheaper and offer many of the same amenities. If you are willing to put up with a little inconvenience by driving or busing to the parks, it is a LOT cheaper. I have stayed at all the mods except CBR and I prefer POFQ.
Beth, mom to older DD (8/01) and younger DD (10/06) and always missing Leah (4/22 - 5/1/05)