So I always wondered this, (and please be kind I did have a child who did pass away) do you have to file for a dependent who passed away? Or how does that work?

If that decedent is required to file a final return then the person in charge of their final arrangements must file it.   https://www.irs.gov/taxtopics/tc356

If this is a child that is your dependent then you can still claim them in the year of death if they qualified as your dependent while they were alive.

So very sorry for your loss.   In order to answer you, we need more information.   You say your child passed away.  When did that happen?   If your dependent child was still living in 2021 the dependent can still be claimed on your 2021 tax return--as long as the child otherwise met the criteria to be claimed as a qualifying child or qualifying relative.  So---are you asking if you can claim the child on your 2021 return?   Or are you asking about the 2022 return you will prepare and file next year in 2023?

Or are you asking if a final tax return needs to be filed in the child's name?   Did your child have taxable income in 2021?   Or in 2022?

@3c5e380e0950 - basically, in the year of death, the requirement to file are the same rules as if they were alive.  The only difference is that the administrator of the estate is signing for the return and if there is a refund due, the IRS has another form required (along with the need to submit the death certificate to prove it).  

if this person was a dependent of someone else, then that someone else can still claim the deceased individual for that year of death.  Again, the rules for claiming a dependent in the year of death are the same as if they were alive that year.