They said the tech giant has "clear policies" on what responses its AI chatbots can offer, and said its policies "prohibit content that sexualizes children and sexualized role play between adults and minors".
"Separate from the policies, there are hundreds of examples, notes, and annotations that reflect teams grappling with different hypothetical scenarios," they said.
Senator Josh Hawley, a Republican from Missouri, announced he was probing Meta in a post on X on 15 August.
"Is there anything - ANYTHING - Big Tech won't do for a quick buck," he said.
"Now we learn Meta's chatbots were programmed to carry on explicit and "sensual" talk with 8 year olds. It's sick. I'm launching a full investigation to get answers. Big Tech: Leave our kids alone."
Facebook, WhatsApp and Instagram are all owned by Meta.
