The best way to plan for this situation will vary from family to family. Assess the risk of this realistically, and remember that both you and your spouse will face the same risk.
If it is important to you that your children get something when you die, you could name them in an insurance policy or use the proceeds of an RRSP.
It is also possible to set up a “life interest” in a property, such as the family home, whereby your spouse will be allowed to live in the home for the rest of his or her life. Then, after he or she passes away, the will can provide for the children to inherit their share of the house.