Question

Two parents have an eye color of blue. What percentage of their offspring will have blue eyes?

Answer 1

All of the children will have blue eyes. Blue eyes are recessive, therefore if both parents have two copies of a recessive gene they will each pass one copy and the only possible outcome is a homozygous recessive trait for the child.
Note: this is not actually true in real life as eye color is more complicated than that however this is what is taught in textbooks and what answer your teacher will look for.

Answer 2

Each child has a 25% chance of having brown eyes and a 75% chance of having blue eyes. This is simplified since the other eye color genes (like those that influence green eyes) are being ignored. But it does mean that brown (or green or hazel or…) eyes are a definite possibility for these blue eyed parents