Are children born outside marriage treated differently under Ontario's intestacy rules?

No. Ontario's intestacy rules treat children equally regardless of whether their parents were married. A child born outside of marriage has the same right to inherit from both parents, and both parents have the same right to inherit from that child, as if the parents had been married. The Succession Law Reform Act does not distinguish between "legitimate" and "illegitimate" children.

This reflects broader changes in Ontario family law, which moved away from distinguishing between children on the basis of their parents' marital status. What matters is the legal parentage of the child — whether they are recognized in law as the child of the deceased.

Where parentage is disputed or unclear — for example, where a putative father never acknowledged a child — a determination of parentage may need to be made before inheritance rights are established. Courts can make such determinations in appropriate cases. If you want to ensure a specific child is recognized in your estate plan, naming them explicitly in a will is the clearest approach.