This isn't the first time I've heard of this happening and yes, it's pretty creepy if you ask me. I've also seen posts where this is happening with multiple providers. Let's see if we can get to the bottom of this. To start, what type of phones are you and your daughters using? Are you using the stock messaging app or are you all using Hiya? If you're all using Hiya, I'd recommend switching to the stock messaging app to see if this happens there as well.
Am getting a lot of those too everyday and it is so annoying - I added those random numbers to be "NEVER ALLOWED" in T mobile's
Family Allowances but these random senders with random numbers keep texting.