Mark Twain National Forest is really really big. It more or less starts in St Louis and runs diagonally down to the s.w. part of Missouri. It drifts over I44 for a part but mostly stays south of it. There are some good spots to see from St. Louis to Branson, Hermon south.
St. Louis of course has the Budweiser Brewery. Herman is an old German town to look into https://www.lazydaycampground.com/ this campground is a great place to call home when visiting Herman. Although Herman does have a good looking city park, I have never stayed there.
Then theres Branson with all sorts of things to do. We have alot of great RV parks here and really to many to mention. The COE is a great park as is Americas Best. With three of you, you may want to make reservations early.
As for whats in between its really hard to say.
Come and enjoy
Itasca Meridian SE 36g
Road Master Tow Dolly