Clark sent Andrew Price Jr pictures and video of the helpless babies during a nearly-three-hour rant of horrific text messages after she suspected him of cheating.
Among the messages she wrote:
"You better pray for your kids" and "I'm killing them" before signing off with a laughing emoji with tears in its eyes.
In one video she films the girl lying face down on a bed before she pans to the boy in the same position.
"Ahh, look, Angel is still alive and sweating. Your son on the other hand is not even breathing," Clark can be heard saying on the video, before adding: "I wish I could keep the camera still."But Mr Price allegedly replied,
"Send it to the cops post it to fb (Facebook) idc (I don't care) anymore you ruined my life," according to a police affidavit.
Coleman McDonough, superintendent of the Allegheny County police department, told the Pittsburgh Post Gazette :
"Ms. Clark admitted to smothering her son in an air mattress."
In a series of messages that began on Tuesday around 8.25pm (local time) and continued to 11.12pm Clark says:"I don't want these kids here."
The messages begin with Clarke accusing her boyfriend of cheating on her and threatening to take her anger out on the children.
In one she wrote: "
Ya kids aint safe here. I don't want them here...Answer me or I'm going to jail for child endangerment."
The messages became progressively more threatening and angry until at 10.01pm she messages to say: “So you better pray for your kids.”
: "I wasn't even gonna send you videos but pretty sure ya son is legit dead so...im going to jail either way hope it was worth it."The last messages described in the affidavit came shortly after 11pm, where Clarke admits she "really snapped this time" before adding:
"Sorry i did this i stg (swear to god) i didn't mean to."Emergency crews raced to Clark's home in Hi View Gardens, near Pittsburgh, after Clark called 911 at around 11pm.
But the boy couldn't be save and was pronounced dead 30 minutes after arriving at UPMC McKeesport.His sister is being treated in hospital and police say she is "doing well."