My question involves a child custody case from the State of: Florida

My 2 young children live with me full-time for 2 years now. I recently filed for child support because he hasn't helped to support them but I really want full custody of them and I want their father to have supervised visitation.
I started keeping my children from their father because he is psychologically abusing them. After my daughter has a visit with him, she comes home crying and extremely upset because he says bad things about me and then threatens her that if she tells me, he'll be angry and that I will never let her see him again. This is emotionally destroying her.
Since I started keeping them apart, he has been calling me at all hours of the night, leaving notes on my door, and 'messages' on my car. I can't pysically prove it's him but he leaves clues to let me know it's him.
I went to the court house to file for full custody but they said they couldn't tell me what forms to file. How can I find out what I need to file and is my keeping my children from their father hurting my case?