@Jessica *******
honestly mate, if I was you - just do an application for your son/daughter. Add them on as a dependant. So you just go to the application page again, and do an application but just quoting your Dtv as explained above.
Sometimes, the fees for ed visa and hassle can outweigh just having them as a dependant on your visa (you’ve already got one, so it’s really not that difficult and time consuming to approve)
Hope that helps.