What happens if a 3-month-old dog eats dry kibble?

A 3-month-old dog can start eating dry food, because by then its baby teeth are mostly grown and its digestion is relatively mature, so it can digest kibble. But feed puppy-specific food, since at this developmental stage it needs complete, balanced nutrition to grow.

Also, do not overfeed at each meal; about 80% full is enough to avoid indigestion.