If you polled 1000 parents - asked them if they'd rather have those two teenagers, or the adult/parent encounter their kid being kidnapped... I bet most would choose the older white guy.
Very sad to see everyone bitch out. You don't have to go throw a haymaker at the kidnapper. Rather, walk up to them and ask the girl if it is indeed her father. That's not unreasonable. Then call the police if there is any doubt, and maybe grab a few others to help prevent him from leaving with the kid.
The moment the kidnapper has eyes on him - he'll scram. The real dad will stand there and fight with 5 strangers. The kidnapper will flee.