just follow the questions in TT about marital status and then it will ask you about dependents.
you can only be Head of Household if
- you are unmarried with dependents
- you are married but have been legally separated for more than 6 months and you have dependents. That word "legally" means different things in different states.
It is not necessary to file as Head of Household (HOH) to get the Child tax Credit. You can file as Single or even Married Filing Separately (MFS). You cannot get the Earned Income credit if you file as MFS, but can with either HOH or Single.