Feel free to msg me for more help in Chicago- we're lifers here and it's not all that bad.
If the RV is new to you, I would head in from Ohio towards Urbana, IL then take interstate 57 North towards Chicago. This is the easiest way into the area without paying told and coming the way you are, though it is longer than I-65.
Warrenville has a nice campground open on weekends at Blackwell forest preserve- book early. The other camping options are good too- anything private is further out.
Rather than renting a car, or dealing with the inconvenience of the train (www.metrarail.com), if suggest you take Lyft to get around. The train is cheaper/ free for kids, and a nice experience- but you need to be comfortable navigating between stations, Gates/ tracks, etc. And they run less frequently than in the weekdays.
Once downtown, all the suggestions are good and there are plenty more in guidebooks, online, or message me. With the challenges of an RV in Chicagoland, you may just prefer a hotel, or try an alternate destination- like Amish / RV areas around Elkhart, IN.
Enjoy your trip!
PartyOf5 appreciating our Creator thru the created. 5 yrsL 50k, 49 states & 9 provinces.
May you find Peace in all you endeavor.