If you take the northern route, you can go through Vicksburg if you like Civil War history. We have also stopped at the beach in Pensacola.
A good stopping point is Daphne, Alabama. It's close to Mobile which has a battleship and submarine you can tour and also Belingrath Gardens which is gorgeous but probably better for an older family.
We haven't stopped too much since this is a LONG trip. Bring lots of snacks and car games.