I'd load up a pre-paid debit card and send it to him. He can use it at almost any "network" ATM in Germany to take out cash (which is almost all of them). Or to buy stuff at stores.
Send him the PIN in e-mail, separate from the card.
You can send such a card through the mail via normal mission channels. Put it inside a Christmas card and write your grandson a nice note about how you're glad that he's seeing the world and to buy himself and his companion something fun.
They'll probably spend the money on food: regular meals if they're undernourished or junk food and cheap restaurants otherwise.
Of course, one would have to send the gift by post, not through the mission home. And there is likely now a mission rule against missionaries giving you their physical addresses.
I have sent money through the mail, but it isn't insurable or declarable by the USPS. You'll have to hide that from the postmaster to get it posted.
What would work better IMO, and get there more quickly would be to wire it to your grandson. You'd need to let him know what the tracking #; so once it's there he can go pick it up. It's relatively inexpensive, and gets there a heckuva lot quicker than snail mail (without the added worry of theft or missing mail, that won't be covered by insurance if it disappears.)
Gift cards are tricky when sending them international - plus the added fees associated with using them ie, surcharges etc. They also are not accepted universally, which is another downside.
Whereas a wire transfer gets there quickly, easily, and can be picked up at the nearest Western Union office to the missionary. It will be automatically changed to the euro currency so you won't have to do that either.
Edited 2 time(s). Last edit at 11/15/2017 08:58PM by Amyjo.
A wire transfer or Western Union "send" might be a good idea.
However, I just wanted to point out that even 10 years ago, I went all over Germany and never found an ATM that didn't accept my debit card. They're all on either the Plus, Star, or Interlink networks. And the surcharges were less than in the US. :)