Tooth decay or staining?

[Olivo]

I noticed tonight some brown on DD's back teeth. She is 5, we brush for her. Can tooth decay come on very quickly? She was at the dentist do a checkup less than a month ago and I was told all was well. Could it be staining, or odd I need to get it checked? It seemed to be all her upper back teeth.

Worried bump.

My DD is due a check up next week.
She is 3.7 and has some staining on her front teeth. No idea what it's from as she doesn't eat lots of sweets and we do a proper tooth-brushing session.
Dentist confirmed last time (about 6 months ago) that it was staining and not decay.

Could your dentist advise over the phone if you're worried?

Yes I might be able to call, it is just so hard to get hold of each other during work time! Two visits ago she had a bit of staining which the dentist cleaned off. Really hoping this is. The case, if it is decay, she can't wait till her next visit in February ??