Here's the problem with every ride-on you've bought so far: it fit one kid for one year. The 12V was perfect at four and a joke at six. The fast one was great for the nine-year-old and terrifying for the little one. So you bought another, and another, and the garage filled up with plastic.
GritRider has a high/low switch on the console. Low caps it around 5 MPH — a four-year-old with some ride-on time can drive it. Flip to high and it runs up to 8 MPH, which is where the seven-to-ten-year-olds live. One machine, every kid in the house gets a turn, and the speed is your call, not theirs.
The gas pedal is variable, not an on/off button, so they roll on power like a real car instead of slamming into it. There's a real brake pedal, not a lift-your-foot-and-coast. Two seats with seat belts built in, sized for two kids up to about 69" tall and 130 lbs combined.
That's the whole point. The four-year-old starts on low this year. In two summers she's on high. The nine-year-old is driving now, and the six-year-old inherits the driver's seat when he ages out. You buy it once, and it's still the right ride-on when the youngest turns ten.