Just as any audience presents certain challenges and affordances, new considerations must be made when designing effective sites for a young audience. However, it is often difficult for an adult designer to accurately remember what it is like to be 10 years old, and so it is important to turn to research conducted with children and teens to get a sense of their preferences.
The Nielsen Norman Group conducted two separate usability studies with children (ages 6-12) and teens (ages 13-17). Based on the results of their two studies, The Group compiled 70 design guidelines for developing more usable sites for children and 60 guidelines for developing for teen audiences. While much of what they found is intuitive, other findings offer new and interesting insight.
(Related: Evaluating the usability of educational websites for children)