Canada has updated their requirements to account for partially vaccinated children

https://travel.gc.ca/travel-covid/travel-restrictions/covid-vaccinated-travellers-entering-canada#determine-fully

If you qualify as a fully vaccinated traveller, your unvaccinated or not fully vaccinated children must follow specific requirements when you return to or enter Canada. This applies to unvaccinated or not fully vaccinated children under 12 years of age who are accompanying a parent, step-parent, guardian or tutor who qualified as a fully vaccinated traveller when they entered Canada.

These requirements also apply if you are returning from a short trip of less than 72 hours.

Unvaccinated or not fully vaccinated children under 12 must complete pre-entry, arrival and Day-8 tests, unless you have evidence that the child had a positive COVID-19 test taken 14 to 180 days prior to arrival in Canada or the child is under 5 years of age.

For the next 14 days, the children must also:

  • not attend school, camp, team sports or daycare
  • not attend large or crowded settings, indoors or outdoors, such as an amusement park or sporting event
  • not take buses, subways, trains or other crowded transportation
  • not attend a setting where they may have contact with vulnerable people (e.g. long term care facility), including people who are immunocompromised, regardless of that person’s vaccination status or public health measures
  • stay in a place that allows the child to avoid all contact with any person that:
    • has an underlying medical condition that makes the person susceptible to complications related to COVID-19
    • has a compromised immune system from a medical condition or treatment; or
    • is 65 years of age or older
  • limit contact with others:
    • remain with their fully vaccinated parent or guardian, as much as possible
  • wear a mask and physically distance when in contact with non-household members