Hi,
just a few ideas..
You can get 'magic cream' sorry i don't know the medical name, which is applied 10-20 mins before an injection that helps the area.
you can also get a teddy with a certain company that's like a diabetes buddy! or get a teddy from anywhere then he can give his teddy a pretend injection then you give your sons his?
you could also test your blood first to try encourage him to see it is a little painful but if you can do it he might feel better after seeing you...
I'm not sure how old your son is but involving him in the care could make him feel special, like him inserting his own test strip into the machine, that's if he's old enough.
It must be quite scary for a child! hope it goes more smoothly soon!