Books:
The Gifted Kids' Survival Guide by Judy Galbraith
101 Success Secrets for Gifted Kids by Christine Fonseca
A list of kid-friendly sites for curious learners:
Hoagies' Gifted Page for Kids and Teens
Wonderopolis
Kids.gov
Discovery Kids
The Artist's Toolkit
Free Rice
Multiple Intelligences
Brainy Kids
Neuroscience for Kids
Ask a Biologist
Brain Boosters
OLogy for Kids