A series of clues typed out onto index cards that can be given to a group of children:

A. Charlie's Number

C1: Charlie's number is palindromic, the second and third numbers are different.
C2: Charlie's number is greater than 100 and is prime.
C3: Charlie's number is odd. The difference between the largest and smallest digits is 5.
C4: Charlie's number is less than 1000. The sum of the digits is 14.
C5: Charlie's number is not divisible by 3. It is less than 500.
C6: Charlie's number is a whole number with only two divisors.

B. The Tower Block

C1: There are six blocks in the tower, a yellow one is at the top.
C2: The red block is above the green block.
C3: One of the yellow blocks is above the green block, the other is below it.
C4: Each of the blue blocks shares a face with the green block.
C5: No two blocks of the same colour touch each other.
C6: There are no brown blocks in the tower.

Similarly, almost any shape/solid that is constructed can be represented as a set of clues for children to work with. En route, an opportunity to develop listening skills, a reasoning facility, as well as encourage the thoughtful selection and discrimination of materials.