A surveyor is going around houses to collect some information for the government.

At one house, he meets a woman who has three children, and he asks her for the ages of the children.

The woman replies: "The product of their ages is 36, and all three have integer ages. I would give you the sum of their ages, but it wouldn't help you".

The surveyor responds: "I still don't know their ages".

The woman tells him that her oldest child just started taking piano lessons.

What is the difference between the ages of the oldest and youngest child?