They have different toys than you. Different parents. Sometimes they can give you a piggyback ride, which is awesome. They can build anything out of legos. They are ready made friends, who you've known your whole life.
I forgot that if you leave your purse on the floor by a crawling baby, they will get into it. And she needed to make some calls. Check her facebook and stuff.
My kids only have 4 first cousins, which is kind of a tiny number around these parts. Especially since there are so many kids in my family. My sister and I are the only ones with any offspring so far, and David's only got one brother who has yet to marry and reproduce.
Growing up around your cousins is fun and fulfilling, because it guarantees some sort of playmate at most family functions. When you have a cousin who's only 3 weeks younger, you've always got someone who thinks your jokes are funny and who you can refuse to share your toys with. Ava doesn't have anyone that close in age, but Brinley is only one year younger, so eventually she'll catch up and be ready to have some adventures too.
Playing dress up, eating chapstick, watching wimpy kid movies and giving bunny ears to people while hiding behind them in the picture are only a few of the adventures they've had recently. I'm sure they'll have many more and get into their share of trouble.