This is because dataTable["data"]["children"]
is not a dictionary, it is a list:
>>> dataTable = {'a' :1, "data":{'b':2, "children":[{'c':3, "data":{'d':4,'e':5, "likes": 'null', 'f':6} }] } }
>>> type(dataTable["data"]["children"])
<type 'list'>
If you want a specific item from the list, get it by index:
>>> dataTable["data"]["children"][0]['data']['likes']
'null'
If you want all children, iterate over the list:
>>> for child in dataTable["data"]["children"]:
... print child['data']['likes']
...
null