Fortunately, I haven't noticed any challenges with my vegetarian son. He is 6 years old and currently in 1st grade.
I have educated him on the reasons why it is not only compassionate, but healthy to adhere to his diet.
He has always been a vegetarian and it seems that he is influencing other children who are wanting to eat compassionately and healthy as he does.
Many of those whose lives are filled with loving energies and do not follow the norm become leaders for others to follow.
You may find the following link helpful:
http://www.lifedynamix.com/ebooks/HealthyVegetarian.pdf
Good luck and thanks for spreading the message of compassionate and healthy eating with your son :)
The world will be a better place because of you!