Agreeing with many others that it's usually less a matter of having lots of money, and more a matter of prioritizing. Yeah, there are some people who're really rich who stay onsite, but for the most part, it isn't that they're really rich but that staying onsite is really important to them. Important to the adults, at any rate.
I guess I have to bite the bullet and "do it for the kids", save my money for in the future when they are older and then stay at WL when they would appreciate it more.
Be aware that a lot of kids don't care. There are many angry parents who kick out the cash for onsite, and "the kids don't appreciate it."

In one of my Timeshare groups, whenever someone's going to one of the Orlando resorts the first time with kids the age of yours, they're advised to
not buy their tickets ahead of time if the vacation is "for the kids," because so many kids who go there just want to hang out at the really cool pool and do the onsite activities.

And it's not even one of the coolest offsite choices!
Same with some kids and the Disney resorts -- they'd just as soon stay at the resort, play in the brilliantly themed pool, do the onsite activities, maybe do a character meal at one of the other resorts, or visit the other resorts for fishing (Riverside) or riding water mice (bunch of them) or a Pirate cruise (different bunch of them). If we stay in the Animal Kingdom Lodge in 2015, that's what we'll be doing. And your kids are the ideal age for that.

The challenge, of course, is for the adults to be that close to the parks, and not go.
But if you want to do it "for the kids," skipping the parks and doing other stuff onsite is a possibility. Depending on what you do (the magician and juggler at Boardwalk cost nothing, for instance) and when you go (off season there can be some great deals on room reservations), staying onsite without doing the parks could be cheaper than an offsite resort with the parks. My kids at those ages would have found the parks overwhelming, but would have loved the fantasy of some of the resorts, and it wouldn't have been a hardship for hubby and I to avoid the parks; only you know how that'd work for your family.