What you need to print:

• 2x Bolt.stl
• 2x Wheel.stl
• 1x Sitting_Area.stl
• 1x Frame_left.stl
• 1x Frame_right.stl
• 2x Little_wheel
• 2x Little_wheel_with_axis.stl

What else do you need:

• 2x small screws to connect Wheel with Bolt (print only version broke after 5min handed over to my kids). I used 8mm x 2mm screws.
• a little bit of glue for sitting-area + both frames and the little wheels