I really hate to see inexperienced people, no matter how dedicated, get land turtles or tortoises. They are NOT easy to keep, ...they just take a long time to die when you keep them poorly.
You may be a perfectly rational human who takes great care of your animals, but most people just can't seem to handle the commitments required for a land turtle or tortoise (they live a looong time, hopefully outliving YOU if you take care of them). So, in general I'm against them for most people.
Additionally, turtles aren't toys. They don't appreciate handling. You might have a hard time explaining that to a 7yr old.
If you do decide to go that way, read, read, read and then read some more. Don't get a wild caught animal, and be sure you are obeying local and state laws (many states outright ban the possession of native species like Box Turtles or Sliders). Don't get something like a Leopard Tortoise or (God Forbid) a Sulcata Tortoise. They live too long and get far too large for any normal family.
If you want a turtle, I'd say get a water turtle like a Reeve's Turtle. They stay small, have amazing personalities and can live in a more reasonably sized aquarium. While they are easier to keep, no turtle is an "easy keeper". For water turtles, you'll usually need serious filtration. For most of the common native species, like a RES, you usually need a somewhat larger tank. Also, be aware, they do eat meat.
Let me recommend Melissa Kaplan's site
for info, caresheets, and links.