If you forgot your Apple ID (your Apple ID is usually your email address), click here --> https://support.apple.com/HT201354
"If you forgot your Apple ID password" click here --> https://support.apple.com/HT201487
What to do after [or even better, before] you change your Apple ID email address or password - https://support.apple.com/HT204071
If you still need help:
Contact Apple for help with Apple ID account security "This article provides country-specific Apple Support contact information for customers seeking help with their Apple ID password or other security-related issues."
https://support.apple.com/HT204169
or
Contact Apple for support and service - "See a list of Apple phone numbers around the world." - https://support.apple.com/HT201232
If you set up a young child's account see this: Family Sharing and Apple ID for your child - https://support.apple.com/HT201084
- "Your email address is the rescue email address for your child’s account, and you can use it with the security questions you provided to reset a forgotten password. You can keep your your child's account more secure with two-factor authentication."
- "If you need to see the options you have for managing your child's account, you can sign in with their Apple ID and password at privacy.apple.com."