12 inchers
Here's my 3yo in her spiderman outfit on her half-pint sized bike.
Next pic is of my 12 in bike "Misty". That seatpost is actually an old flat steel 22.X mm handlebar that had some funky bends and no bulge in the middle.
I today had to make "Misty" fit Riley (swapped out the ape hangers for someflat bars, and put a small post/saddle back in) because we left her bike out at the house we are house-sitting at.
She was still ripping up the neighborhood on that choppered out sh!itbox.
All that said, you guys have built some damn fine bikes for you kids. I obviously need to get my act together and ditch the clown bike in favor of something bad-A.