i can't comment on the accuracy of his diagnosis since i can't examine your child but a three-year old who has been vaccinated with the chicken pox vaccine can certainly get painful shingles. it doesn't happen very often but i do see this several times a year in my busy clinical practice.
my 3 yr old has been diagnosed with shingles he has never been exposed to chickenpox and has been vaccinated. how is this possible? sores started on the back of his neck (itchy) then started down the left side of his back also one on the right shoulderblade and on the the left side of his face near the ear there is no red rash or fluid- filled blisters just scabby itchy sores.