Orders made under provincial family law (in Ontario: Child, Youth and Family Services Act, Children’s Law Reform Act, Family Law Act) have no automatic authority on reserves, which fall under federal jurisdiction.
As a result, if you get an order under provincial family law, you may have difficulty getting it enforced if you and/or your ex-partner live on a reserve.
If you live on a First Nation or your children will spend time there when they are with their father, it will be important to consider approaches to your safety and arrangements for your children that minimize the opportunity for your ex-partner to take advantage of enforcement challenges.