Did you have any trouble setting up and using the card? Which card were you using? I'd like to find a 32g with eye-fi and geocaching class 10. I guess a 16g would do. I know it's just me. I love gadgets and pushing things beyond their limits.
I have a Sandisk Eye-Fi without geocaching 8GB class 6 IIRC, to have it working with ML need to use EOSBoot or MacBoot since the firmware upgrade method don't works.
I bought it in a place where they accept returns in 5 day, to return it if it was not working with ML, maybe you can use the same approach.
For geocaching I use a gps logger on my android phone and when importing pics they get geotagged.
I didn't bought the 16GB because I prefer more small cards than only one big, to reduce the risk of loss of data.
And your guess is right, no grandchildren here around

If eye-fi and ML work on you camera, with the iphone you can find apps for geocaching and importing your camera pics, and share them from there. I think the return option is the best way to test it before keeping the card.