Having just tried to renew my sons debit card without much success on the USAA site, I checked the chat topics and found that someone else (many someones actually) has already identified this as a problem back in May of 2014. Since it's not fixed yet, I'll review it for the next victim in the hopes of saving some pain for them:
Your kid's replacement debit card will come with instructions to activate it via phone or website. If you're on the West Coast and it's dinner time (the only time you ever end up dealing with this stuff) you'll find that the USAA offices are closed. Next, you can try the online instructions asking you to choose an "activation" option from the "I want to" list that does not exist. Allegedly, despite the instructions included in the envelope and on the card itself, you do not actually have to activate the card (which is kind of interesting...)
A big thank you to the person who posted before me, as it helped us out and now we can enjoy dessert!
USAA - please fix this bug, it's annoying and an easy issue to resolve.