Sharing iCloud storage between family members
Update 2017/2018: It appears Apple finally allows sharing iCloud storage between family members (see the newly accepted answer). Glad to hear it!

Original:

The correct answer is No, there is not.  Apple does not let you share iCloud Storage with family members, unfortunately.

Here's a forum link where this has been discussed:

https://discussions.apple.com/thread/6543858

You can share your account and password, but then the storage is yours and not really sharing with a sub-account. Each individual Apple ID gets their own paid/gifted/free storage quota and any one account can bump up their storage only and it doesn't affect any other AppleID storage capacity - family membership regardless.