It could be very real the pain that your child is feeling, and that it is not just him being upset of having a needle in him.  It all depends on the guage, length, and the type of IV that is inserted in your child.  You should insist that they use BD IV catheters made out of vialon.  Vialon is a patented material that conforms to the curves of a vein, and reduces pain because of that.  It is generally used on babies, the elderly, or people who are chronically ill.  It is a little more expensive than then the IV’s made out of your standard teflon, so hospitals are not always ready to take them out to use on their patients.