I am worried about something similar. In 2018, I didn’t claim my children as dependents, their mother did. She filed her 2019 earlier so she got her stimulus but it didn’t include our two children. My accountant just filed my 2019 on Monday, I claimed my two kids on my 2019. I am worried we will miss that $1000 because he waited so long to file and they’ll go off my 2018 return instead.