I assume you are in Springfield and want something within four hours of there. Chicago, St Louis and Indianapolis are all good options but I bet you have thought of those. I don't know if you have ever been to the Starved Rock area but it is a beatuiful park. They have a lodge there which is nice. There is also a new hotel which looks like a lodge that supposedly has an indoor water park in it. I don't remember the name of it but I saw it when I drove by in Sept. Lots of outdoors stuff though like trails and such so I hope the cold doesn't bother you too much since it will be Feb. There are lots of nearby little towns that have stuff to do. Great Itlaian food in Lasalle/Peru area. Princeton is right down I-80. Nice main street area with shops. There is also an old covered bridge there. Not a place I would go for a week but an extended weekend should be good. It's about two hours north of Spfld.

Grand Bear Lodge by Starved Rock State Park - wonderful! Indoor water park fun for all ages (We had 4 generations in the water at once!). Arcade and indoor amusement park with plenty for the 8 year old, not so much for the toddler, tho. We didn't eat at the GB restaurant, but the actual Starved Rock Lodge has the best breakfast buffet we've ever eaten! You might consider letting your 8 yr old bring a friend. Also, more room choices the earlier you book, so don't wait! We're going back again this year.