I've used the handle bars on that type of kids bike for extending the height of handle bars on a slightly bigger BMX kids bike. I just welded one on top of the others and had 4 hand grips, 2 lower and 2 upper.
As for tires I found useful from the same kiddie bike for beefed up brackets to hold them to my off roading motor bike that has a dual purpose to eventually make it to Burning Man in the dressed up form as a California Sheepshead Fish. Its gonna look for krill in the 50,000 year old dry lake bed at 8000ft.
The build continuing
Out on USDA Forest Service Roads where Lic. OHV OK'ed