We say that charge is quantized , what about the quarks, having +_1/3 and +_2/3......, fractional values.......

The actual definition of Quantization is the smallest value that can
exist & "exist stably"..
In case of Quarks, they have charge e/3 or 2e/3 but they
do not exist alone..
They exist in triplets...
For example, proton is formed of 2e/3 , 2e/3 & -e/3 making
charge e.... while neutron is formed of 2e/3 , -e/3 & -e/3 becoming
neutral...
Hence, e is the smallest charge that can exist.... therefore quantization
of charge is e..




If one quantizes a scalar complex field (Klein-Gorden field), then we get the charge of the field as Q(sum of k)(a+(k)a(k)) where a+(k)a (k) is a number operator which will take integer values.So for any field the total charge is an integral of Q.KG field refers to spin zero particles.For spin 1/2 particles, one must quantize spinar field.Again the total charge of the field will be integral of Q.