If your child doesn’t yet need to file a tax return, you can leave the Net Income (T1, line 23600) and Total split income from Line 68360 of form T1206 boxes set to 0.00. Just remember to answer “YES” to the question ” Is [Child]'s income zero?”
If you have TurboTax Live Assist & Review, here is how to talk to a Tax Expert: https://turbotax.community.intuit.ca/community/navigating-turbotax/help/i-m-using-turbotax-live-assist-review-how-do-i-talk-to-a-tax-expert/00/873764