you can definitely reapply and don’t cite the reason that she is coming to look after the older child/support you, just mention that u want to reunite and she hasn’t ever met your second born…if you mention that she is coming to take care of your first born then definitely its a red flag that she is taking away someone’s job in canada!
make sure you show enough funds(in her account if applying for visitor visa n in yours if applying for super visa), properties in her bank, stress that your dad will not be accompanying, if she has job there its details etc, also if applying for visitor visa, just show the duration of visit in weeks(say3-4) and not in months(it’ll be a red flag again)
many who had previous rejection have successfully got approved this time..all the best to you too