I made this puzzle for my grandson for his 2nd birthday. I made the puzzle pieces with multiple colors by pausing the printer at the appropriate level and changing the filament. Dremel has an unpublished pause command (G5) that I used to pause the print. The tires were printed separately as was the pin. The pin is a press fit to secure the tires to the puzzle pieces. All the tires freely rotate.
I have also uploaded a generic ABC board and eliminated the text. You can print out the ABC board without text or add your own.
I designed it using Fusion 360 and printed it on the Dremel 3D45 printer using HatchBox PLA. I used a combination of Dremel's version of Cura and the Simplify 3D slicers.