If i paid my brother who is 15 to watch my son can i add him as a care provider for the dependent care credit ?

[Opus 17]

The child's uncle can be a qualifying caregiver.  If care was provided in your home, the person is your household employee and you must issue them a W-2 if you paid them more than $2200.  You must also include them on your tax return (schedule H) as a household employee and pay household employee's tax (social security and medicare).  https://www.irs.gov/publications/p926

If you paid them to provide care in your their home, you don't need to issue any tax paperwork.  

[Edited to correct typo]

In either case, you must include their SSN on your tax return, and the IRS may look to them to report matching income.  (If most cases, they will owe little or no tax unless they have other jobs or investment income in their name.  

If they are your household employee, you might have to follow state laws regarding household workers wages, hours and working conditions.  You would have to check your state laws on that. 

[DianeW777]

Yes, if you meet the requirements as shown below.

 Here are the rules for the person you are paying to care for your dependent son from the Form 2441 Instructions.

Who Can Take the Credit or Exclude Dependent Care Benefits? You can take the credit or the exclusion if all five of the following apply.

1. Your filing status may be single, head of household, qualifying widow(er) with dependent child, or married filing jointly. If your filing status is married filing separately, see Married Persons Filing Separately, later.

2. The care was provided so you (and your spouse if filing jointly) could work or look for work. However, if you didn't find a job and have no earned income for the year, you can't take the credit or the exclusion. But if you or your spouse was a full-time student or disabled, see the instructions for lines 4 and 5, later.

3. The care must be for one or more qualifying persons. See Qualifying Person(s), earlier.

4. The person who provided the care wasn't your spouse, the parent of your qualifying child, or a person whom you can claim as a dependent. If your child (including stepchild or foster child) provided the care, he or she must have been age 19 or older by the end of 2021, and he or she can't be your dependent.

5. You report the required information about the care provider on line 1 and, if taking the credit, the information about the qualifying person on line 2.

As noted by our awesome tax expert @Opus 17, if the care was in your home then you will be considered a Household Employer.  Follow the instructions provided.