How can my friend get her kids back?

My friend went through a rough patch last October dealing with money and other issues, so to help her out her ex-boyfriend, whom she has two children with offered to take her two boys for a while to help her out. She lives in Ontario and He lives in Alberta. He said he would bring them back in January. They have joint custody through the court system, with primary residence with her in Ontario. She called him in January to arrange a time to get her boys back and he told her that he isnt going to give them back. He owes way over $10,000 in child support and is now trying to take her baby bonus, saying its because they live with him, and gst. Her boys want to come home and he wont even allow them to talk on the phone with her. He even wont allow her oldest son to go on his facebook so she cant even get ahold of them. My friend has tried to call the FRO in dealing with the owed child support but there is no way to get ahold of them it goes to voicemail. She wants her children back and he is 100% refusing. How can we go about getting them back, because he is in a different province does that cause a problem? We have called the police and they say they cant arrest him or anything because it doesnt say they can in the papers. She cant afford a lawer and we could try legal aid. Isnt there someone we can call to help? How does he get her baby bonus for those two children if he owes her so much in child support over the years, which by the way he is refusing to pay. HELP!