You might try buying the BOB clothing from Goodwill type stores in sizes too large. Unfashionable clothing may discourage pillfering.

Some have said they buy sweat pants and shirts because they can be worn oversized and the drawstings allow for smaller sizes. They are unisex so can be handed down to younger kids without worry of gender sterotypical clothing issues.

It would work for me since I hate sweat shirts/pants and never wear them anytime ever.

Sounds like a training issue for your wife. Stop raiding the BOB's. You might try using a cable tie to secure the zipper of the bag. At least you would know it had been raided when you picked it up because the cable tie would have to have been cut.