Phone number linked to Kids T-Mobile Sync Up Watch

My daughter has a T-Mobile Sync Up Watch. There is a phone number associated with it.  She is wearing it to summer camp. She is able to text and call me from her watch. She texts me, and I can text her back. She can call me, and I can call her.  But occasionally I am getting messages from someone else (NOT my daughter), but it looks like she's sending it because it shows up under her name. I verified that it's NOT her sending those messages. 

There were a few different messages telling me that I'm texting the wrong person. But it's showing up in the chat with my daughter. When I call that phone number, my daughter answers. 

Has anyone had this happen?!  I have no idea what to do!