Nonsense

The total number can be broken down to 6 * 1,000,000 + 6 * 100,000 + 6 * 10,000 + 6 * 1,000 + 6 * 100 + 6 * 10 + 6 * 1.

So you could think of it as a number with 6 millions, 6 hundred thousands, 6 ten thousands, 6 thousands, 6 hundreds, 6 tens, and 6 ones.

They just wanted any 7-digit number with 6 ‘ten thousands’ in it, eg: 1,060,000.

Putting a six in all of the positions fulfilled the question’s requirements without actually proving whether or not they understood the question.

The number one in 10,000 is in the 10 thousands place. In the child's answer, the number 6 is in the 10 thousands place, which isn't clear since they're all 6's, but the bracketed number here is the 10 thousands place [6]6,666