> X + Y + Z ≤ 10 (the sum is two digits) I don't understand this part. Surely every number between 10 and 99 (inclusive) has two digits? And numbers <10 have o

> X + Y + Z ≤ 10 (the sum is two digits) I don't understand this part. Surely every number between 10 and 99 (inclusive) has two digits? And numbers <10 have only one digit? Have I forgotten how to count to 2? If we use your interpretation then the fact there is an oldest child is redundant; but if we don't then the fact that the sum is two digits is redundant, and there are multiple solutions. The 'oldest child' thing rules out 6, 6, 1 as the answer, but afaict 18, 2, 1 and 12, 3, 1 and 9, 4, 1 and 9, 2, 2 and 6, 3, 2 are still valid solutions as well as 4, 3, 3.