You need to wear gloves when you pick blackberries.
We have them growing wild in our side yard, and last year my DS found child sized gardening gloves for DS. So when we go out to just pick a pint or so of them, he has to go through the production of finding the gloves, and putting them on, and making sure they are on all the way, etc etc etc. All this for a 5 minute exercise. But hey, he enjoys it.