The process of opening a TD account, then linking your bank, then mailing in your paper bonds and have them posted to your TD account can be quite lengthy (several months). However, once you have them in TD and your bank connection is established, the process of cashing in the bonds and the money showing up in your bank account is (on government timescale anyway) blazingly fast. A couple of days, maybe.
So, have your son open a TD account and convert his whole stash of paper bonds to electronic. After that, everything will be fast and, I would say EASY in the future.
As someone else pointed out, an added bonus of the electronic bonds i s that they will send you e-mail reminders when the bonds stop accruing interest. The paper bonds just sit there until you remember to check their date.