Jack is also a kind of "Everyman" name (or everboy, in this instance.) "Every man Jack of them."
It is still a popular name. In our case the actual name is Jacob, but we call him Jack after his great-grandfather. So if you want less common, Wally would be the choice. Kids may associate that name with Wall-E the Disney robot, who is both innocent and heroic.
Just saw the above post, which I second.