If I filed taxes before that child credit was passed. Can we still apply for it?

The enhanced child credit has not passed.  It is in the Senate.  It has not  been passed or signed into law.   

The additional child tax credit for tax year 2023 has not passed.

The legislation passed the House but has not been voted on by the Senate nor has it gone to conference committee nor has it been signed into law.

If the credit is eventually passed and if it retroactive to 2023, we still won't know how the IRS will handle it.  They might require taxpayers to file amended returns, or they might re-process affected tax returns automatically.  You will just have to wait and see.