Break it into these five statements:

#1.  My FIRST digit is 1 less than my SIXTH (or LAST) digit. 
#2.  My FIRST digit is 8 greater than my THIRD digit, 
#3.  My FIRST digit is twice my FIFTH digit.
#4.  My FIRST digit is 4 times my FOURTH digit. 
#5.  My SECOND digit is 0.
What number am I ? 

Make 6 blanks for the digits.

                      `


Use statement #5 to fill in the SECOND digit as 0.

     0                `


Statement #4 tells us that the FIRST digit is either 0 or 4 or 8, for those
are the only ones that are 4 times a digit.

Then statement #2 narrows it all the way down and tells us that the FIRST 
digit is 8.

Also it tells us that the THIRD DIGIT is 0.
So fill those in:

 8   0   0            `

Then statement #1 tells us that the SIXTH (or last) digit is 9
So fill that in:

 8   0   0           9`

Then statement #4 tells that the FOURTH digit is 2
So fill that in:

 8   0   0   2       9`

Then statement #3 tells us that the FIFTH digit is 4 
So fill that in:

 8   0   0   2   4   9`

So the number is 800249,  Hope this helps you explain it to your child.

Edwin