My son does sprints on my roadbike (with flat pedals), does fine and kills the transitions. +100 on proper bike size and a fitting, makes all the difference in the world. If you think you might really get into it I'd pony up for at least 105 groupset otherwise you'll be buying a new bike within 8 mos. like I did. It's definitely not a cheap sport but can be affordable if you hunt around a bit on ebay/amazon/etc. I bought used cycle shoes, pedals, helmet and a couple kits my first year and saved a bunch. Have fun man, racing with your kid is always worth it.