Use 1, 2, 0 and 4 to form the smallest decimal with three decimal places. '0' cannot be omitted.

The smallest decimal number with three decimal places using the numbers 1, 2, 0, and 4 is 0.124. Here's how you get it:

1. The smallest number should start with the smallest non-zero digit. So, the first digit is 1.
2. The next smallest number is 2. So, the second digit is 2.
3. The next smallest number is 4. So, the third digit is 4.
4. The number 0 cannot be omitted, so it is placed before the decimal point.

So, the smallest decimal number with three decimal places using the numbers 1, 2, 0, and 4 is 0.124.