my boyfriend and his x divorced in 04 and at the time he received full custody she was not employed so there was not a child support order at the time. However ever since then she has harassed and tried to claim income tax refunds on the children that she also was never entitled to and recently she has pursued this harassment heavily. I was wondering can he try to collect back child support from her for all of these last few years since she hasn't helped raise the kids any... and only seeks to cause trouble.

Please pay more attention to posting guidelines. There is a Read First sticky in the Divorce forum (where this was moved from) that directs questions of a legal nature to this forum.

If no support order was issued then you can't ask for back support.

There is no child support, even due, if there was never a court order, so you can't sue for something that was never given