Hi bing li!

To protect the privacy of younger users, users must be at least 13 years old to participate in discussions on Khan Academy, which may be why your child does not have access to post questions in the discussion sections. If your child is over the age of 13 and meets all of the existing discussion requirements but is still not able to access discussions, their birthday may have been incorrectly entered—if that is the case, instructions for changing your child's settings can be found here: https://support.khanacademy.org/hc/en-us/articles/204795250-How-can-I-edit-my-child-s-settings-

I hope this helps! Please let me know if you have any further questions. 

Oops. Wrong conversation!