Why am I not getting the $2000 child tax credit for all 3 of my children? It's awarding for my 17 year old and 8 year old, but not my 9 year old.

Yes, your nine-year-old should be eligible for the $2,000 tax credit (assuming all other criteria are met). ‌However, your 17-year-old isn't eligible for the credit.‌ So, you should be receiving two $2,000 Child Tax Credits, and two $500 Credit For Other Dependents.

If your nine-year-old is the child with the $500 credit (not the 17-year-old), revisit the entry for them. ‌Here's how to do this in TurboTax Online:

1. Navigate to My Info, Your household, select the first dependent. 
2. Choose "My child", continue and be sure their name, date of birth and proper citizenship is complete. 
3. Continue, and answer the question about living arrangements and parents. 
4. Continue, and answer any less common situations, if applicable. 
5. Lastly, enter the child's SSN and be sure that "Not valid for employment is printed..." is NOT checked.