In this situation, you would not be seeking a child custody modification, but rather you would be requesting an initial child custody determination. (raleigh-divorce-lawyers.com)
(8) «Initial determination» means the first child custody determination concerning a particular child. (familydiplomacy.com)
Limiting factors in child custody determinations involve quite complex legal issues which need the attention of a seasoned professional — a child custody lawyer. (purplelawfirm.com)