If I'm understanding your post right, symbols/emojis are appearing in your messages even though you didn't type them. I know how disruptive it would be to experience complications with your messages, so I'm glad I have the opportunity to help you with this.
Have you fully restarted your devices lately? If you haven't, try restarting them to see if it clears up the problem. Restarting is a very simply step that can solve a lot of various issues. If your iPhone and iPad aren't running the most current version of iOS (11.2.6), another good step would be to update them. Even though this is not guaranteed to be a resolution for what you've been experiencing, it's always a good idea to be running current software to ensure your devices run as smoothly as possible. Before updating, I recommend backing them up first. You can find the steps on how to update, and how to back up, in these two support articles:
How to back up your iPhone, iPad, and iPod touch
Update your iPhone, iPad, or iPod touch
If the issue persists, reply back with your answers to the following questions:
- Is this happening in the stock Messages app that comes with your iOS? Do you experience any issues with your keyboard and/or typed text in any other apps?
- Are the symbols/emojis already typed in the text field when you open a thread? Or do the symbols/emojis appear in your sent messages only?
- Do you have any third-party keyboards downloaded to your devices?