No, the Canada Revenue Agency (CRA) will not automatically add your dependents if you forgot to put them on your taxes. If you have already e-filed your taxes and realize you have forgotten to include your child-dependent information, you must submit an adjustment to your tax return after you receive your Notice of Assessment (NOA), as suggested by the CRA.
To make a change to your tax return, you can use the CRA's "Change My Return" service through your CRAMy Account, or you can complete and submit a Form T1-ADJ, "T1 Adjustment Request". You will need to provide the correct information about your dependents on the adjustment request, and the CRA will review and process your request.