M.G.
I always have this problem since we are military...now that my son is in school we invite the entire class...yes...we don't know them all especially since his bday is in Sep (the beginning of the school year). So invite them...this is a good way to meet them and their mommies.
Good luck...and I do know how you feel...you feel bad for you son...and this will change and before you know it will have a network of friends for you and him.