Cognitive in the sense it's on the same developmental path as functions such as reasoning and speaking, rather than emotions or social. if it's a poor choice of word then go ahead and substitute a better one.

Maybe capacity is a better word. Whatever the right word is, babies don't have the ability to even recognize themself in the mirror, or even their own body when an infant. I think the idealization in a child is on the same path-they don't have the ability to experience complex emotions and thoughts.

This explains better:
www.psychology.emory.edu/cognition/rochat/Rochat5levels.pdf