There's two things you can do. In the PlayOnline Viewer at the FFXI title screen, you can go in the Content ID's menu and try to "Reactive Content ID."
If that doesn't work, you can always try calling POL, and mention something about your little brother accidentally deleting your first character.
Other than that.. I assume you deleted the character on the current Content ID, which would cause the first method to not work at all. (Can't hurt to try.)
Or you can wait for a "Return to VanaDiel" campaign event, but to be honest.. might take a long time for that to come and then it's still doubtfull that would work.
So the best thing you can do is call PlayOnline Support I guess.
I'm sure you had a good reason, but why did you delete your first character in first place? Was it because of the extra $1 a month for a second character?