I'm going to be the odd one out I'm sure, but I'm a big advocate for barefoot running, so I say keep kids in soft soled shoes forever. Kids have proper foot strike, and wearing hard-soled shoes changes that. I wear soft-soled shoes even as an adult and I'm slowly learning proper foot strike again. Studies show that people have fewer foot/ankle/leg injuries with soft-soled shoes.
Happy atheist, vegan, punk rock-loving scientist. Wife to the love of my life Matthew (SAHD), mom to DD "E" (4), baby boy "K" (2). Proud stepmom to DSS "M" (26)