The correct answer is option 'A', the 1st separate Rock Edict. Let's break down the answer and provide an explanation:

1. Introduction:
The question asks about the source that contains the pronouncement "All men are my children." We need to identify the specific source among the given options.

2. Understanding the sources:
a) 1st separate Rock Edict
b) 2nd separate Rock Edict
c) 5th Rock Edict
d) 6th Pillar Edict

3. Identifying the correct source:
To determine the correct source, we need to analyze the content of each option and find the one that contains the pronouncement "All men are my children."

a) 1st separate Rock Edict:
The 1st separate Rock Edict is one of the earliest edicts issued by Emperor Ashoka, a Mauryan ruler in ancient India. This edict has been found in various locations across the Indian subcontinent. It primarily focuses on the principles of dharma (righteousness) and moral governance. The pronouncement "All men are my children" is indeed found in this edict, making it the correct source.

b) 2nd separate Rock Edict:
The 2nd separate Rock Edict is another edict issued by Emperor Ashoka. However, this particular edict does not contain the pronouncement mentioned in the question. Therefore, it is not the correct source.

c) 5th Rock Edict:
The 5th Rock Edict is also an edict issued by Emperor Ashoka. It primarily discusses religious tolerance and the promotion of various religious practices. It does not contain the pronouncement mentioned in the question, so it is not the correct source.

d) 6th Pillar Edict:
The 6th Pillar Edict is one of the major edicts issued by Emperor Ashoka. It focuses on the promotion of dharma and moral governance. However, it does not include the pronouncement mentioned in the question, so it is not the correct source.

4. Conclusion:
Among the given options, the 1st separate Rock Edict is the source that contains the pronouncement "All men are my children." This edict by Emperor Ashoka emphasizes the idea of universal brotherhood and the king's responsibility towards his subjects.