Chicago to Hilton Head

My brother-in-law is traveling from Chicago to Hilton Head, SC later this week, stopping for one night each in Louisville, KY and Pigeon Forge, TN along the way. They'll be in Hilton Head 5 days, with possible side trips to Savannah or Charleston. On the way back, they're stopping in Charlotte, possibly back through Louisville, but the return trip route is up in the air.

He's traveling with his wife (they're both fairly adventurous eaters, but more him than her) and two kids under 10 who aren't particularly adventurous.

The kids being there would restrict their choices more than money, to an extent (and usually more expensive is less kid-friendly anyway.)

Any advice on where to stop, where not to stop? Would you recommend Savannah or Charleston? And what route would you take on the way back?

In Louisville, Lynn's Paradise Cafe is a fun, quirky stop that may be worth considering. The atmosphere is rather noisy and festive, but in a well-behaved sort of way. The food is hit and miss: some things are great, other dishes are just so-so. It can get really busy, though, so your BIL may want to call ahead and reserve a table. The gift shop at the the front of the restaurant has a lot of fun and unique stuff (bacon candy, librarian action figures, etc.), but not all of it is appropriate for kids.

Great trip. Both Charleston and Savannah are for sure worthy them exploring. Savannah is very close to Hilton Head and there is much more interesting food in Savannah than Hilton Head. If they choose to go to Savannah I would be glad to recommend places.
A few suggestions:
 
Breakfasts"
Clarys
B. Mathews.
 
Subs/Pizza
 
Screamin' Mimis
 
Other places;
Sweet Potatoes
Tanners- Chicago hot dogs and Italian Beefs
 
 

hilton Head- Harold's Diner
Pigeon Forge-Smokey Mountain Brewery
Charleston-Poes & Homny Grill
Charlotte- Pinky's Westside Grill, Chicken Box, Mac's, BBQ King just to name a few