Bbm."Kidnapping" is just a euphemism for abducting a child. A child will not understand they are being lured away into a dangerous situation. Children cannot consent to "relationships" with adults. The victim's mother reported her as missing numerous times, which further emphasizes my point that the mother did not allow or consent for her child to go with this man. You can be abducted without force if you are groomed by your adult abuser.
Agreed 100 % about children cannot consent.
Not so sure about that (the bolded) because the reporter who spoke to her brother said that he (the brother) said the family was aware of Celeste seeing this man.
For how long were they aware ?
It's important, in my opinion, because if it was ongoing, I have a problem with that.
Red flags and all that.

Missing girl, 15, identified as dismembered body found in D4vd's Tesla
The dismembered remains found in singer D4vd's Tesla have been identified in a bombshell new development.
Celeste's mother said she believed her daughter matched the description police had provided, and that she had had a boyfriend named David.
From this snipped portion I think it's possible that even if no consent was given by the mother which we do not know, this relationship may have been allowed to go on for too long ?
Still so many unanswered questions.
Imo.