Yes. If your child qualifies as a dependent you can amend your already filed return to add the child. To qualify as a dependent your child must meet the following guidelines:
1. The child must be a US citizen, US resident alien, US national, or a resident of Canada or Mexico.
2. The child must be your child, stepchild, foster child, or a specific relative.
3. The child must be under 19 or under 24 if they are a student.
4. The child must have lived with you for more than half of the year.
5. The child did not provide more than half of their own support.
6. The child is not filing a joint tax return. This is mostly for older children.
As long as your child can be claimed as dependent per the guidelines above, you can file an amendment to claim the child as a dependent. If you originally filed with TurboTax, you can use the information here to get help on filing an amendment: How to file an amended return.
