How sign iPhone into child’s Apple ID

I’ve created an Apple ID for my child to use on a iPhone 8, but the child’s iPhone 8 will only prompt me to sign into my Apple ID/iCloud account. How do I sign into the child’s Apple ID/iCloud account on the 8?

Context: when the 8/child’s phone is signed into my iCloud account, it is automatically populated with my texts, contacts, calendars, etc. I have done a factory reset on the child’s phone & set up her own child’s Apple ID under my account’s family sharing “Set up children’s account” option. I need to prevent the child’s phone from having all of my information on my iCloud account, not delete apps on the child’s phone to prevent access (child needs to use text/calendar/contacts/email apps).

Any quick answers out there? Thank you for reading my question.