These are circumstances that allow a claim for carers allowance, you must get or be on:-
* Attendance Allowance * Disability Living Allowance at the middle or highest rate for care * Constant Attendance Allowance at or above the normal maximum rate with an Industrial Injuries Disablement Benefit * Constant Attendance Allowance at the basic (full day) rate with a War Disablement Pension
My previous post applies to all jobseekers who are looking after a member of the family who is ill, regardless of what rate of DLA the member of the family is in receipt of.
Hope this information is of some support to you and your son.