Facebook asks me to send a text "f" to this number for identity verification, but I get a message back saying that this is not a valid 10-digit mobile number. In the mean while, my account has been blocked for 2 weeks

Wow that is over protective. and if you do confirm the number what next. Your searching for what seems to be another child and you are an adult. Ask your child who it is. if you dont like who they talk to take the phone away. Dont Look for and harass some child. SMH

Found number on childs phone. Trying to confirm owner.