I finally got this to work. I had to log my kid out from the parental controls on my phone.
I used to get messenger notifications in my FB messenger inbox. I clicked on one of those and it led me to click Parent Dashboard. Another way to get to the Parent Dashboard is by clicking on the three horizontal lines in the corner of your FB Messenger App > Settings > Visit Parent Dashboard. Once there, you can click on your child and you'll see an icon at the top that looks like a gear with the word "Controls" next to it. Click that, then look for "log out of devices." I had to log out of her iPad even though it was a new iPad, deleted the app and downloaded it again, she was still considered to be logged in. Once I did this, I went back to the messenger kids app and started over from the initial setup. It flowed right into her inbox! I hope this helps.