Have the owner and pup at whatever distance is initially comfortable for pup, with the pup on a loose lead or held loosely by the collar. The owner has no treats because the child has them all. Then, throw the treats about 1 inch closer to the child each time, with the owner continuing to click each time the pup is just about to grab the treat. If pup begins to ignore owner and stand and wait for next treat from child, hallelujah. Then let child take over the clicker, until the pup and child live happily ever after.
Next session have the pup go a bit closer.
Stop the exercise. This is preferably done off leash in enclosed area. Gradually, have child stand up which means, of course, that you may have to go back to original comfortable distance and repeat the exercise, but it progresses much faster at this point. No matter how wonderful the outcome, this will need to be repeated with the same child and other children for several weeks in different places, until the pup can get past its fear enough to be really socialized to kids. Every child and adult in this pup's immediate future should be handed treats by the owner, and offered at a comfortable distance from the pup.