Coaches see it all the time: kids arriving at the hill in boots they simply can't flex sufficiently to get forward over their skis. In most cases, they'd be better served by less-expensive, softer-flexing models. Don't leave the shop until you find a boot your child can clearly flex without a struggle. Another common mistake is sizing too big, either to get two winters out of a boot (impossible) or to give the child "wiggle room" for warmth. The fit should be quite snug in the shop. Boots get roomier with use, and one that's too roomy robs its wearer of control over the ski.