How important to you is free dining? Keep in mind that as your kids get older, free dining may become even more important to you because the cost of the
DDP climbs every time one of your children turns ten (as does the cost of feeding kids OOP once they are 10). You also have to consider that you won't be able to book one room at WL, AK or the moderates (besides POR) once your youngest is three. Even the deluxe rooms that sleep five get crowded as children get bigger. Some people don't mind the cramped quarters, some do. You won't be able to sleep five in a DVC studio if all kids are 3 and over, and some of the 1BR villas only sleep four. Some 1BRs have sleeping space for five - AKV, BLT and OKW.
We have never been a DDP family, not even free dining because it is rarely available when we travel, and we got to the point of wanting more space when we stay on site. That is why we bought into DVC. We aren't really saving money, but we are getting larger accomodations with a 2BR villa for about the same per night, a little more, than we were paying to stay at a deluxe resort with a nice discount. We have three kids as well - 12, 10 and 7 - and everything, including Disney, gets more expensive as they get older!
I don't regret buying in 2.5 years ago, but it is a large amount of money to commit to spending at WDW each year - you'll have the DVC annual fees, tickets, food and airfare each year. Sometimes I look at that amount and wonder if we will continue being happy spending that much every year. Start with calculating how much you'll spend with DVC compared to what you are spending now and definitely research buying resale to save money.