Why is a 6 year olds SSN not valid for employment

Does it say that on your child's Social Security card?   Look at the card.   Do you see that on the card?

It sounds like you may have accidentally checked the box indicating it was not valid for employment- you can go back to My Info to correct this.

Navigate to My Info, Your household, select your dependent. 

• Choose "My child", continue and be sure their name, date of birth and proper citizenship is complete. 
• Continue, and answer the question about living arrangements and parents. 
• Continue, and answer any less common situations, if applicable. 
• Lastly, enter the child's SSN and be sure that "Not valid for employment is printed..." is NOT checked.