Your Money, Your Child — Not Their Spouse: How to Protect Your Estate from In-Laws

You’ve worked a lifetime to build your estate. You want it to go to your child. Not your child’s spouse. Not your child’s ex-spouse. Not a divorce settlement you’ll never see coming.

It’s a wish that comes up more often than you might think in estate planning conversations — and it’s completely legitimate. The good news: with the right legal tools, it’s absolutely achievable. The bad news: a basic Will won’t get you there.

Here’s what you need to know.

The Problem with a Simple Will

Most people assume that leaving money directly to their child in a Will means it stays with their child. Legally, that’s often not the case.

In most Canadian provinces, inheritances received by a spouse during a marriage are classified as “excluded property” — meaning they don’t get split if the marriage breaks down. So far, so good. But there are important catches:

The growth on the inheritance is not excluded. If your son inherits $2.5 million and it grows to $4 million by the time of separation, that $1.5 million in growth can be subject to equalization under Ontario’s Family Law Act. His spouse may be entitled to half of that gain.

Commingling kills exclusions. The moment an inherited asset is mixed with marital property — deposited into a joint account, used to pay down the matrimonial home, or transferred into a shared investment — the protection may be lost entirely. What was once clearly excluded becomes legally murky.

Death changes everything. If your son or daughter predeceases you, the inheritance passes under their Will or the intestacy rules — which may put everything straight into the spouse’s hands.

In other words, a direct gift to your child looks clean on paper but can unravel quickly when life gets complicated.

The Most Powerful Tool: A Testamentary Trust

A testamentary trust is created inside your Will and comes into effect at the time of your death. Rather than transferring assets outright to your child, the estate flows into a trust — a separate legal entity — and your child benefits from it under the rules you set.

Because the assets are legally owned by the trust (not your child personally), they generally fall outside the definition of “net family property” for equalization purposes under Ontario’s Family Law Act. A spouse cannot make a claim against assets that your child doesn’t legally own.

Here’s what a well-drafted testamentary trust can do:

• Ring-fence the inheritance so it never becomes marital property
• Control distributions — specifying when, how much, and under what conditions your child can access funds
• Protect against creditors as well as spouses
• Specify what happens on your child’s death — directing any remaining assets to grandchildren rather than a son or daughter-in-law
• Survive a divorce — the trust continues even if your child’s marriage ends.

A testamentary trust is one of the most effective estate planning strategies available to Canadian parents, and it’s significantly underused.

Adding Explicit Exclusion Language in Your Will

Even if you don’t use a full testamentary trust structure, Ontario’s Family Law Act allows a Will to specifically state that an inheritance — including any income and growth generated by it — is excluded from the child’s net family property for equalization purposes.

This kind of exclusion clause is a standard tool in estate lawyers’ arsenals and can provide meaningful protection on its own. It won’t protect against all scenarios (particularly commingling), but it signals your intent clearly and creates a legal basis for protecting the inheritance if your child’s marriage breaks down.

Think of it as a floor of protection. A testamentary trust is the ceiling.

Encouraging a Domestic Contract (Prenuptial or Marriage Agreement)

This one requires a family conversation — which is why many parents never pursue it. But if you’re concerned about protecting a significant estate, encouraging your child to enter into a prenuptial agreement (or a cohabitation agreement for common-law partners) is one of the most direct solutions available.

A properly drafted domestic contract can specifically exclude inherited assets, together with any growth and income they generate, from equalization on separation. It can also address what happens to those assets if your child dies first.

Many estate lawyers strongly recommend this approach where shares in a family business or substantial wealth is involved. As one legal professional put it plainly: most parents don’t want their child’s ex-spouse as a co-inheritor of a family legacy.

The conversation may be uncomfortable. The legal protection it creates is not.

A Note on Quebec

If you or your child lives in Quebec, the rules are different — and getting more complex. Under the Civil Code of Quebec, inheritances are technically excluded from the “family patrimony” that gets divided on separation. However, they can become a debt owed to a spouse if inherited money is used to improve shared family assets.

As of 2026, Quebec’s new “Parental Union” rules (following Bill 56) have extended inheritance and property rights to common-law partners who have children together. For the first time, these partners may have a claim on an estate even without a Will. This makes clear, explicit estate planning language even more critical for Quebec residents.

What About Common-Law Partners?

Many parents focus on married spouses — but common-law relationships are increasingly relevant, especially for younger generations. The rights of common-law partners vary considerably by province. In Ontario, common-law partners have no automatic right to equalization of property (unlike married spouses), but they can make claims for unjust enrichment or constructive trust if they can show they contributed to the growth of an asset.

If your child is in a long-term common-law relationship and your estate plan doesn’t address it, you may still face unexpected exposure. A testamentary trust protects against this scenario just as effectively as it protects against a formal marriage breakdown.

The Conversation Nobody Wants to Have

Here’s the real challenge: protecting your estate from a child’s spouse often means having a frank conversation with your child about it — or at minimum, making decisions that could affect family dynamics after you’re gone.

There is no single right answer. Some parents are comfortable using a trust that gives their child full access and flexibility, using the legal structure purely as a shield against equalization. Others want tighter controls. Some want to have the conversation openly with their child and encourage a domestic agreement. Others prefer to let the legal documents do the work quietly.

Whatever your approach, the key is intentionality. The estate plans that create the most family conflict are the ones where the parents’ wishes were never clearly expressed — legally or otherwise.

Your Smartwills Takeaway

You cannot simply assume a Will protects your child’s inheritance from their spouse. In most provinces, a direct gift offers limited protection — particularly once the money is mixed into a shared life.

The tools that work:

• Testamentary trusts — the gold standard for ring-fencing an inheritance
• Explicit exclusion clauses in your Will under provincial family law
• Domestic contracts — encouraged between your child and their partner
• Gift-over provisions — specifying where assets go if your child dies first

None of these requires you to distrust your child’s partner, or even to involve them in the conversation at all. They simply reflect the reality that life is unpredictable, marriages can fail, and a lifetime of accumulated wealth deserves a thoughtful plan.

Your legacy is yours to protect. Make sure your documents actually do it.

Check out our post on the frustration of having a legitimate legal document rejected by a financial institution