It appears that printing the children's notes is not an option for the Ancestor Book report (is that the report you're looking at?). The Options screen is the same for all reports, so it's a catch-all rather than what's possible for any particular report.
I have to wonder, though, why you would want to print the notes for the children in the section for their parents? You can select the notes to be printed in the next generation where the children are listed.
I'm not the last word in all things Legacy, I'm just the admin of this board who's had a little practice with the program and tries to help where I can. You may have good reasons for wanting to include these notes with the parents, and I'd be interested in hearing your arguments here on the board if you care to share.
In any case, if you would like to make a suggestion to the programmers, see the link "Suggest a new feature" on the Home tab in Legacy to do so.