Welcome to WikiTree - Bienvenu à WikiTree!
I love that you are a new member, and immediately offering sources for your information.
You have a couple of options for fixing this.
You can send a message to the profile managers for J-F using the "send private message" link, highlighted in orange, where you see the profile managers listed for his profile. They may or may not choose to act on your information.
You can enter a public comment on the left margin, which will post the information for others to find if they look, and it will generate an email to the profile managers. The profile managers, or other WikiTree members who see the comment, may or may not choose to act on your information.
If you are a WikiTree member you can also add the missing child yourself. First you click on the "Edit" tab on J-F's profile, then you can see a link called "Add/Remove child" on the right hand margin beneath the list of existing children. You simply add the information you have into the template and press "save". Once the profile is created, you can edit and add to it as you learn. There are good instructions and tips in the help menus, and lots of us on G2G who will help if you run into a snag.
If this is an ancestor of yours, then you may want to consider adding him yourself. This will let you add other missing family members and build your tree into WikiTree. Its natural to be nervous at first, but the wonderful thing about a wiki is that mistakes can be fixed, So you don't have to worry about doing it perfectly while you are learning.
Profitez de l'aventure,