I just introduced my 3-year-old niece to pin trading this summer. To make it easier for her I started her with 10 pins...5 different pins and a duplicate of each. So, she had one Minnie pin to keep, and one duplicate Minnie pin to trade away. One Mickey to keep, and one to trade away, etc, etc. It helped her get the hang of it without being upset about giving something away. By the end of the week she totally understood how it worked and traded even those pins that she didn't have duplicates of. Plus, she felt like a big kid with her very own lanyard. It's a great hobby and some 3-year-olds will definitely enjoy it. Have fun!!