Welcome to HealthcareMagic forum.
on face of children could be due to varied conditions ,some minor like eczema,pityriasis alba
or post inflammatory scarring
and leukoderma while others which need definitive treatment like tinea versicolor
or hansens disease or vitiligo .
Your child could have a risk of vitiligo if the spots are depigmented and spreading without any antecedent cause or trauma to skin. if they are hypo pigmented and spreading it could be still eczema or infection ( tinea).
Since your child has been examined by his physician and advised a referral to a dermatologist
,It is definitely recommended to get a confirmed diagnosis.
Remember that whatever is the diagnosis , the earlier the treatment started the better is the outcome.
So please do not worry and get a dermatological evaluation before jumping to any conclusion.
Hope I have answered your query.
Wishing you good health.