WHITE SPOTS ON FACE IN KIDS - waxing & waning with season

We call them pityriasis alba. They are actually of nonspecific origin and mostly do not require any treatment except moist cream/lotion. When they have excess scales/reddish hue/cosmetic problem, one may occasionally use low potency topical steroid creams.

And just to mention, there is no study that suggests its correlation with worms or calcium deficiency.

Severe hypo-pigmentation could be vitiligo which has to be treated under care of a skin specialist.