If your child earned any income from an employer, they should have received a T4 slip, which reports their employment income and deductions. If their employer withheld any taxes from their pay, they may be eligible for a refund if they file a tax return.
If your child earned income from self-employment or as a contractor, they may need to file a tax return and report that income.
Even if your child is not required to file a tax return, they may want to consider filing to claim certain tax credits or benefits, such as the Canada Workers Benefit (CWB), which provides additional income support for low-income workers.