Q: Why is my text messages going to child phone

because you're using the same icloud account! make a different icloud account for your children! it's the imessage

Best not to use the same Apple ID, configure Family Sharing instead.

Set up Family Sharing - Apple Support

If you want to use the same iCloud account, you can go to Messages in Settings on your child's phone, and choose what messages the phone receives. You can do the same on your phone, to see what you are receiving.