The 3 year old child's safety is paramount, and if it were me involved in this situation somehow, her well-being would be my top priority. Everything else will shake out from there.
Because you've seen a lot of potentially/actually dangerous situations involving the child, you need to find out if you are a "mandatory reporter". A "mandatory reporter" means that either certain groups/professions of people are
required to report
any suspicion of child abuse, or that
anyone, regardless of profession, is required to do so. Check this link to understand more of what you may be required to do:
https://www.childwelfare.gov/pubpdfs/manda.pdfThe section titled "Standards for Making a Report" gives details on when a person must report (italics mine):
Typically, a report must be made when the reporter, in his or her official capacity, suspects or has reason to believe that a child has been abused or neglected. Another frequently used standard is the requirement to report in situations in which the reporter has knowledge of, or observes a child being subjected to, conditions that would reasonably result in harm to the child.
Reports and reporters are generally anonymous, depending on what is reported and what state you're in.