DeMartino took to Twitter to apologise, telling followers that the move "wasn't thought out completely".
Fellow YouTuber Petty Paide uploaded a video in response, titled "Gabi DeMartino must be STOPPED!"
Paige accused DeMartino of "normalising child pornography" and asked "what the f*** was she thinking?".
DeMartino came in for heavy criticism on Twitter, where some said her actions undermined the fight of abuse survivors to remove child abuse material from the internet.
"There are victims of child abuse and porn out there who are fighting for their photos and videos to be removed from the internet and Gabi Demartino is sexualising one of herself as a toddler and uploading it herself for money," said one outraged Twitter user.
Another said: "She knew what she was doing. She is 25. She sold child porn. It's a crime".
Adult entertainer Iana Evans told the Daily Beast that she had contacted the FBI over the incident.
"I have a circle of people who call me when there are 911s, and this was a 911,"she said.
"There's no excuse for that. Apparently, the way she advertised it on her OnlyFans page was that she would get naked, and this is someone who doesn't get naked. And then people clicked on it and it's a video of her as a 3-year-old child not putting her panties back on?
"It's women like her that do this that make people turn to those of us in the adult industry who would never do something like this, and we take the blame for it. It's shocking. Just shocking."