They're sturdy, stable with a low center of gravity and go slow. It's perfect for a first time battery operated ride toy. With an easy on/off pedal and handle bars right out in from of you. A 6v quad is an excellent option for any little one that hasn't had much or any experience on an electric ride-on. My son went from a quad foot to floor to 6 volt quad with ease. He already knew how to steer it so now all he had to do was make it go with a button instead of his feet. :-) Easy!
We had a little inexpensive no name brand we paid around $80 bucks for. It was called the "Tazmanian Devil" though it was so tame. He loved it and we enjoyed watching him ride.
Background is an image of my daughter posing on daddys quad. Not quite ready for that thrill at the time but sitting on it was pretty fun too! It was a 700 Bormbardier I believe. In back of her is my son passed out in my Polaris Ranger. Oh how we do love our ride on toys! :-)