Want to build an kids electric "jeep"...ideas?

My kids have used a powerwheels jeep for years, however they are getting bigger and need a bigger "jeep". I do have an old riding lawnmower that I want to use. I want to keep it electric, and use some deep cycle batteries. Question is what do I use for the motor/motors? I imagine the motors from the original jeep would burn up in no time. I've thought about wiper motors or even starters but wonder how long they would last and/or the batteries. it would be nice if a charge lasted for a few hours if possible, then I could just swap batteries. How does the original jeep hi/low range work? Any ideas welcomed! Thanks