You're going to have an awfully tough time finding a halfway decent kids' road bike for $100. I bought my daughter's for $40, but had to do LOTS of work on it and replace a whole bunch of parts. After powder coating, parts to build a new wheelset, and various other stuff, I'm probably in it for at least $250.

...and that's without brifters, which are the most expensive part of a lot of bikes nowadays. But speaking of brifters, I'm not a big fan of the Shimano STI shape for small hands. The brake pivot's pretty low, which seems like it wouldn't be the easiest thing to squeeze with pre-teen hands. Heck, they're the hardest lever to work on any of my bikes even with my average-sized adult hands. The Tektro RL341 short reach levers are much easier to grip, as are Campagnolo levers. SRAM levers have a reputation for working well with small hands, too. (If you're shopping Campy and SRAM, though, you're almost certainly out of the $100 price range.)