DH and I frequently drive from the Houston area so we know I-10 well! (Also, I just found this website Interstate Rest Areas
http://www.interstaterestareas.com/!)
The Texas "safety stops" are pretty good now - in addition to clean bathrooms they have picnic areas and little museums and walks where the kids can run around and also maybe learn a little history or nature facts too. I especially like the Chambers County one - it's at exit 814, east of Houston, so a good place for even the adults to relax a little after the stresses of dealing with Houston traffic!
There isn't much in Louisiana. They're rebuilding the welcome station just after you enter LA and I'm not sure when it will reopen. There's another one east of Lafayette, at exit 121.
But Mississippi is great! Plan to stop at exit 2 - big rest area there with space rockets, because it's right across the interstate from NASA's Stennis Space Center. If you have time and your kids are interested, you can visit the space museum that's behind the rest area, the Infinity Science Center
http://www.visitinfinity.com/. There's another rest area at exit 63, shortly before you enter Alabama.
Alabama has a welcome center just inside the state line, but depending on your schedule & ages of your kids you might consider stopping in Mobile to see the battleship Alabama and the other ships and aircraft along with it -
https://www.ussalabama.com/.
Florida is the best - they have wonderful rest areas, generally about 30 miles apart, although some of them are closed for rebuilding (and the highway signs will tell you when you approach one that the next one is closed, so you know not to press on to that next one!). We especially like the one at exit 162, right after you cross into Eastern time. It's up on a hill, very beautiful.
Re staying overnight in Tallahassee - check the mileage and travel time related to how early y'all plan to get on the road, how many hours you can drive, etc. DH and I usually make it to Pensacola or a little beyond, to Milton, but then again we don't leave home until about 9 AM and stop for the day around 7 PM. Tallahassee will be a very long haul from San Antonio - and you lose an hour, too, crossing into the Eastern time zone before you get to Tallahassee.
Have a great trip!
