Here is a large body that totally disagrees with transitioning children:
GENDER IDEOLOGY HARMS CHILDREN
Here is their statement & link to their website.  

The American College of Pediatricians urges healthcare professionals, educators and legislators to reject all policies that condition children to accept as normal a life of chemical and surgical impersonation of the opposite sex. 

https://www.acpeds.org/the-college-speaks/position-statements/gender-ideology-harms-children