SANTA ANA, Calif. (KABC) -- A 21-year-old Anaheim man is facing charges of child abuse after he was arrested, accused of sexually assaulting a 12-year-old girl he met on Tinder.Santa Ana police officers took Sean Rickard into custody Wednesday night. Detectives say the girl was posing as a 19-year-old, but told him her real age before they agreed to meet."He said he didn't care, and they met," said police Corporal Anthony Bertagna. "There was a criminal violation that occurred in our city."Police say the two talked using Tinder and Snapchat for nearly eight months before they met.When he arranged to pick her up from school for a second meet-up, a classmate became suspicious."Some astute student took it up on themselves to take it to her parents, because she didn't feel it was right," said Bertagna. "Outstanding job on her part."Officers took the victim's phone and began to pose as her, setting up the meeting, where they arrested Rickard.While going through the explicit messages, photos and videos they say he sent the victim, they realized he was using a code to avoid detection from her parents. "Do you have homework tonight? She had a specific response - not going to say what it was - so he knew that he was actually talking to the child," Bertagna explained.Santa Ana police are warning parents, as social media continues to advance and change, they need to keep an eye on who their kids are talking to and why."They need to monitor it and monitor it daily," Bertagna said. "They don't want to hear it, they don't want to talk about it, but this is the kind of thing that can happen."