Hey there, Allam!
I just had the same exact same issue for both my sister and I since we file under our parents as dependents.
What you need to do is to;
1) For your kid's file, go to #2 Interview and on the left sidebar, click on "Ontario tax credits."
2) Click on "ON-BEN Application" and click on the +.
3) It will prompt you to look through all the information, but scroll to the final option where it says "Who should receive?" these benefits and simply select let "MaxBack" decide. (This section is about The Ontario Trillium Benefit and Senior Housing Benefits, if I recall correctly.)
4) Click on #5, NETFILE, at the top, and try to file it again for your kid and don't forget to save!
Worked for my sister and I, so hope it works for you!
