Dear Lydia,
unfortunately I can't tell you with full certainty what the reason for the delay is. It is important for you to know if you have submitted all documents. The best way to do this is to contact the family benefits office in charge. Unfortunately, some federal states have experienced delays due to the summer vacations.
In general, you can find out on which day your child benefit should theoretically be paid out by looking at your child benefit number. Please have a **** at this website:
https://***.arbeitsagentur.de/familie-und-kinder/auszahlungstermine?pk_vid=ca8015b93bfbe7981665562673adb8d3
Take the last number: xxxFKxxxxx9 here for example the 9, payment 21.10.
I hope to have helped you with this. Feel free to contact us if you still don't get an answer from the family fund, then we can think again together. In my experience, the offices just always take a little longer to answer.
With best regards
Saskia