I have a child and they are dependent, with a custodial account that had some stocks sold but I can't add it in turbotax in the income section, it does not give an option

you don't include the child's income on your return. the child may need to file their own return (see below) and include form 8615. Turbotax should determine if it's necessary based on what's reported on their return - this requires the parents to complete and file their return since certain info from it is needed for the 8615.

the child is required to file a return if any of the following apply::

1) unearned income of $1300 or more - assuming the child has no earned income,  unearned income would be on line 11 of the 1040 (if they had earned income then line 11 less earned income  - wages or schedule c income )

2) earned income over $14,600

3) gross income more than the greater of (a) $1,300 or (b) earned income +$450 but not in excess of $14,600