Carol, the child support and alimony must be court ordered and you will need the final recorded divorce decree. Also, you will need to show receipt of payments via cancelled checks unless they payment is payroll deducted. Make sure your ex can provide cancelled checks. It varies from lender to lender on how many months of receipt must be documented. I have done it with as little as 3 months.
Also, the end date for child support will be when a child turns 18 even if it may conditionally continue afterwards. So, if a child is turning 15 prior to closing, you will not be able to use that as qualifying income.
Good Luck!