I found one of the "Radio Flyers" w/o peddles at Western Auto for my granddaughter. It's just like a regular trike w/o pedals. It's still in use with my 2.5yo DGS. They are very hard to find. My DDIL found one similar for the 2.5 year old because he couldn't reach the pedals on his big brother's bike that had been saved for him. I haven't seen it yet so not sure what the difference is between the one they already have and the new one.
My DGS can ride the 3-wheeler with pedals (the smaller one).
Oh, they do make the convertible one. Can't remember who makes it...Little Tykes, Fisher Price or Playschool, but it changes from a push trike to a regular trike w/o pedals.