Unfortunately, some phone carriers split text messages automatically depending on the length of the original message. This is out of our control. Click here to read more about this.
This is why we have implemented our 600 character limit.
Having said that, most families will see the messages in the order you send them. One way to avoid phone carriers breaking up your text messages is to send shorter messages. Try sending shorter messages (less than 160 characters) to help address this issue.