weird text messages being sent to my contacts that I did not send

Smart Phones neither have the intelligence nor has the hostility. Hence we need to look at our device settings and the way we synchronise our smart phones with Mac/PC/iCloud and also how careful are we in sharing our sensitive and valuable information with friends and family members.

Be careful when sharing the device's sensitive and valuable information with friends and family members.

Thumb Rules:

1. Enable  Guided Access before handing over an iPhone to kids
2. Don't share Apple IDs
3. Don't Jailbreak
4. Don't share sensitive information pertaining to your device and payment methods

I would change my Apple ID password asap.