When I first got my Dex 6 and had to call support, I was told that the sensor can be off as much as 30%. If something doesn’t seem right, they said to always check the glucometer way. It takes awhile for the Dex 6 to acclimate to one’s body. Calibrate it in the settings to what the glucometer says, if the Dex is way off. The Dex 6 people, however, say not to calibrate it too much.
Try placing on the arms, I know he is little but ask for patches from dexcom next time you call, maybe he is sitting wrong on it or maybe he is a bleeder.