When I was a kid I was better at talking to older kids or adults. Kids my own age were hard to relate to or be serious with. I sort of wish I had younger siblings so then I would know how to cope with younger people.
I wonder if you will buy your cousin/niece something if she asks as you have difficulty saying no. 
I was really good at speaking to adults as well when I was a kid. It was because they would ask the questions and lead the conversation, and I would answer them. I was, and still am extremely polite. It lead to them thinking I was a far nicer kid than I really was, and they put unfair expectations on me. I was just as naughty, if not more so than most other kids, and when the adults realized this they thought I was putting on an act, and pretending to be nice.
My niece is 12 so I'm hoping she's past the stage of asking me to buy her stuff. I will buy her a meal, and let her choose where to go, although being 12 years old she'll probably choose McDonalds
I'll have a couple of friends with me, so they should be able to say no to her if she gets out of control, but she seems like a sweet kid so I'm hoping she won't be a problem.
