At the parks, we don't have characters on ticket cards anymore, we have attractions. If your son really doesn't want a Minnie card, come by a ticket window at any park with a photo of the visual ID (the number on the back of the card that you'd use to link it to
MDE) and tell us his ticket was lost. We'll give him a new card, and only two out of 23-ish of the new ones are "girly" - one has Minnie from a M&G and one has Elsa from the DHS stage show. So your chance of getting a "boy-acceptable" card for him are pretty good.
(Edit: I lied, there's also a Belle card for ETWB, so three out of 23-ish. Still good odds!)