This all sounds very confusing to me.
He has children with three different women, and you have had a child with him, making him a father to four. All the ex's sent him pictures of his children? This sounds like a big mess to me.
Are there any custody and/or visitation court orders in place? Does he pay child support, and make attempts to enforce any rights that he has?
You say that the police are taking this seriously because:
The police have taken it seriously due to criminal pasts with 2 of his ex's partners.
Was he charged with criminal offences? Is this why he is denied contact?
While I think that it is natural for the 9 year old to seek out her father, I get the sense that the mother went ballistic for a reason (who knows her side of the story), and as you said the police have said to stop all contact. Why the 9 year old said what she did is anybody's guess.
Perhaps he could see a good lawyer and enforce visitation (at least) with all of his children, if that's what he wants.