As Branson is a really kid friendly town, in my opinion LOTO is more of an over 21 town. As living in Branson and haved dealt with a granddaughter i would skip LOTO. I travel the 54 route at least twice a year heading north.
A group of folks did the JD Plant in Iowa a fews years ago. For adults its very interesting for young people not so much. I would still go there however.
In Jefferson City the old state prison is well worth the time. I believe a 7 year old would not be bored.
https://www.missouripentours.com/
A stop in Jefferson City would not be complete without stopping at Central Dairy Ice Cream Parlor.
https://centraldairy.biz/
Binder Park is a nice little city park
https://www.jcparks.com/park/binder-park/
Hannibal MO is just a jog off the 54 route and more than well worth the stop. So much for all age groups to do. Could easy spend 3+ days there
Mark Twain caves and rv park would be the place to stay.
https://www.marktwaincave.com/
If you plan on crossing into Wi at Dubuque Ia, Do not miss the Mississippi River museum again very kid friendly
https://www.rivermuseum.com/
Sounds like a very fun trip enjoy the grand kids for as long as you can