We did this three weeks ago ... it was GREAT fun. And I don't think you have to order ice cream for everyone in your party ... but the sundaes are only $6.99 or so.
It's at the Garden Grill, in the Land at Epcot
I made reservations thru 1-407-WDW-DINE
I think we spent about 45-60 minutes, but no one was hustling us out.
We saw Farmer Mickey, Pluto and Chip'n Dale ... the first time around they signed autographs and posed for photos, after that they just "played" with the kids each time around. And I think they each stopped by 3-4 times.
Another fun thing to do with the kids at the Land is the Nestle Toll House Cookie baking ... lower level to the left of the eateries ... best of all it's FREE!!!