I need legal advise ASAP if anyone can help?

looking for some answers from lawyers. My soon to be ex wife had left the children with me in october of 2008 and in august reappeared. agreeing to allow her to see the children every other weekend verbally was working (we have 50/50 custody) until tonight she called and stated that she is taking the kids and not returning them to make up for lost time. My four year old is in school monday through thursday and as other activities and the two year old is just being jerked around by her. The cops said there is nothing they do. My four year old has had an interview with social services in January 2009 (it was taped) talking about his mother hitting him and leaving a bruise on his face. she will not return any phone calls. What legal rights do I have tonight to ensure there safety and get them home with me.