Personally, I've found these to be helpful:
PFLAG - Our Trans Loved Ones pdf
APA - Answers to your questions about Transgender people, gender identity, and gender expression -6 languages available
HRC - Transgender Children and Youth: understanding the basics
Straight for equality - guide to being a trans ally pdf
And some more to your request:
Gender Spectrum - Guide to Transgender Students K-12 pdf
Trans Youth Equality - resources for parents - resource dump for parents of transgender children and youth.
HRC - Explore: transgender children and youth - this is a resource dump for "transgender children, families, and other youth-serving professionals"